I disagree with some of the things you say here, so let's go

Dragon Age: Origins was an epic journey, not the start of one.
The two Bioware games in which the main character was continued into the sequel, Baldur’s Gate and Mass Effect, were clearly set up so the main character would carry over smoothly into the second. Baldur’s Gate made the character a Baalspawn and structured the story entirely around it. Mass Effect made it repeatedly clear that Sheppard is the one of the only people who full understands that Reapers are coming and talented enough to stop actually them.
Dragon Age: Origins however lacks any ongoing personal issues that would be enough to support another game – Morrigan’s child doesn’t count (see below) – and it doesn’t set up some looming disaster that only the Grey Warden can avert. At the end of Origins the PC gathered up allies from across the country and became the only one in history to end the Blight before it destroyed a number of nations. That is epic. There was the problem of the Darkspawn remaining above surface post Origins, but that was taken care of in Awakening. What exactly is left for the PC to accomplish that really can’t be accomplished by anyone else?
First of all, your character is a Grey Warden. Wether they work only against the darkspawn or not, your character is bound to the order and must do whatever it is needed for the order/world. There is a chance the wardens get problems with another nation and enter war, or more things related to the archtect and the darkspawn themselves. Either way, there are several ways to continue the story with your character relating him/her to the order.
But, the setting does set up a looming disaster. The last 2 blights. Repetitive or not, there are two blights to go and many bizarre things around its origin and factors that could speed up the process/slow it down.
And another thing that makes your character special enough to appear again, your character has been one of the few people who engaged an Archdemon in over 400 years. Your character may be the only Warden in centuries to have a noble title or similar position. If that doesn't mean something to you, i'm pretty sure the Grey Wardens think differently (As the treasury woman says in the awakening).
That what our character did was epic, it is true, but was that enough? Even more epic things can be done.
More Morrigan!
Morrigan ending up with a child, god or not, is only one of a number of possible outcomes. Unless the people who want this to be the focus of a sequel also want it forced on as a cannon ending, this event making up an entire sequel seems ridiculous. The plotline being continued as a DLC or subplot of an Expansion for Origins would be a better way to give players a sense of resolution without disappointing everyone who didn’t follow that
plotline.
But then again Morrigan made it pretty clear throughout Origins that the PC would regret forming a relationship
with her in the end. If that PC never finds her, then well, she warned them beforehand. Not all stories need to have a happy ending.
More morrigan is not exactly a problem even for the people who don't like her. You don't like her, don't have her in your party and don't talk to her. And remember that without the ultimate sacrifice there is nothing that much special about her, besides her mother. I can imagine us seeing Flemmeth again as a major NPC in the storyline, but hardly see morrigan as one of the same importance given there are many options. Unless of course bioware decides to make her ending the canon, which i doubt as they already gave us an orlesian warden for the awakening, allowing people who killed themselves to have a new char.
But I do agree that approaching morrigan in a DLC could be better.
But I am so attached to my character and their companions!
And so people want more time adventuring with them? This is understandable, but more for sake of more is
hardly a compelling reason to continue to use them. Posts asking for adventures in Orlais with Leliana or in Antiva with Zevran tend to focus on how utterly amazing it would be to see another area of Thedas with their favorite companion, but gloss over why exactly it is absolutely important for the PC and their companions to be there.
I think it is more important to people to see their companions in the game again, as it gives a sense of reality. I don't think it is that important to the playerbase to -have them in your party- just for the sake of having them. Of course the only exception to that is the romance option.
I don't know about you, but just by seeing Wyne again in the awakening i was jumping like a little girl in bliss. It was a shame her part was small, but the fact she was there and she knew my character (even if it was bloody cold) was a great feeling. Seeing companions again give you a sense of acomplishment as well.
Thedas
The PC from DA: O traveling to another country removes one of the better features of DA: O, the actual origin
stories. The Origin stories in DA: O allowed the player to experience firsthand what it is like to be an oppressed elf in the Alienage or brutality of Dwarven politics, but they also gave the player a connection to areas or people they
would meet later in the game. Without this feature the main character essentially becomes a wandering hero (ine) and removes a lot of emotion for the sake of continuation.
Let’s say in DA: 2 is set in another country like Orlais, which is suffering from a serious threat that could possibly
bring ruin to their nation. Why exactly would the DA: O PC care enough to get involved?
If the answer is that Leliana is from Orlais and you can adventure there with her again, then at that point you are relying on another character’s motivation instead of your own. If that is the case then your character isn’t even needed for the story and just a side-kick for Leliana. (Wait this might be a good idea. Leliana could get her own game.)
A new protagonist with ties to that region through their Origin story would have stronger reasons to get involved than would a wanderer type hero which strengthen the story as a whole. Imagine if DA: O removed origins all together and instead you simply played as a Grey Warden from Orlais. That is essentially what would happen to DA: 2 if we carried over our character.
Just look at Awakening and the number of people who are upset that there isn't enough connections to Origins. Imagine the disconnect of playing your character in another country.
The PC could care about whatever happens in another country for several reasons, connections to their old companions, political reasons, more darkspawn or simply the standing of the Grey Warden order.
For example, if they say: A great evil rises in Tevinter. Part of the playerbase would be like "omg i have to go there, Wyne and Shale are there!" And the ones that simply disliked those two characters could care about Tevinter because the lore is interesting, because of all the secrets, the blood magic and a land free of the chantry.
And they could also care because a warden in that place did someting really wrong or was pleaded guilty for something he/she has not done. Or because the kingdom made a treaty with Ferelden and the King/Queen asked the warden for help, so tevinter would see that Ferelden would indeed be an ally.
there are always reasons why a character would care about a different place, even if they are not directly connected as we were to Ferelden. People don't have to live and die in the same place they were born, they can travel, they can live somewhere else and create bonds that are even stronger. The same can happen in the game and not feel awkard.
And bioware can always give us the option of starting a new character if we feel like it.
Ferelden
If a sequel is set in Ferelden it would be much easier to carry over the protagonist from DA: O into it. At the
end of DA: O the player, regardless of how they acted, would have a lot of connections people and places in the country. Also there is more potential for smaller decisions to carry over through import. Only real problem I see is
having another major event happen there within the Warden’s shortened lifetime that doesn’t feel like it is just an after adventure of the Warden. Those can fit into DLC and smaller expansions.
Before someone says Qunari invasion, Sten never said when it would happen and his people are further north
fighting Tevinter. The Qunari intend to convert everyone to the Qun, his statements could just acknowledge the fact that one day the Qunari will attack Ferelden because of it.
I hardly think they would make another big story in Ferelden, another DLC or expansion sure, but another game? Nah, everything points toward Orlais at the moment. If your character goes to Orlais or anywhere else, sooner or later someone would know that your character was THE warden to kill the archdemon, to kill the hero of ferelden, to burn down a city and etc. And these things can have an impact on how people perceive your character in the other country. I see no problem in importing old saves and inserting the old choices in a new game, even in a different country.
And 30 years is not that little, your character is young, only on his early 20s, his adventuring career just began (The taint would take its toll when your character is around 50). As a grey warden or not, if he was something else your character could die at any age because of the lifestyle. Being a Grey Warden is not the only thing that puts a death setence upon your character. Being an adventurer has pretty much the same risks.
And Qunari invasion is very unlikely to me at the moment, there is too little info on that.
The Warden’s power is over 9,000!
At the end of Awakening or even Origins, the Warden is a beast. Even with the improved AI using more spells and
skills in Awakening, it wasn’t enough to keep up with the Warden even on higher difficulty levels. Unless players are willing to rollback their characters to a lower level with lower level gear, which would be ridiculous for someone who defeated an Archdemon, I really don’t see it working to well.
The warden is indeed a beast, but your character did not defeat and archdemon alone and a game's difficulty is something the developers set, not the story itself. It doesn't matter if your character killed an archdemon or not, if BW do their thing, killing a single genlock could be a nightmare.
They can also change our talents, how many points we have to put into them and etc. It doesn't really matter our level or gear stats, the game will be as hard as BW wishes it to be.
And to be fair, would you really want to start from level 1 again, sweating to kill an revnant when your gear sucks, you don't have access to all these awesome abilities and sweet spell combos? Speaking for myself, i would cry if i started a character without onslaught now because i simply love that ability. I would like to meet more powerful enemies for sure, but not lose the abilities and gear i got.
Pardon any inconsistencies, haven't proof read the wall.
And to finish, i liked your arguments and respect your opinion, but there alaways two sides of a coin ^^