Well, since I already tackled a revolutionary way to do MP earlier in the thread
here, I'll go ahead and tackle co-op, the other MP suggestion most often talked about for the DA series.
Co-op is, in my humblest opinion, not a game seller. It doesn't draw people in. As many people that say playing with their friends would be great, the amount of people who have RL friends that share the same taste in games and also share a similar enough schedule to play together on a regular basis is, just from a statistics standpoint, rather small. Doubly so if the feature is planned as a couch co-op only. So, if a co-op SP portion is included as the MP, I would see it having (needing) to be open to a broad pool of players, instead of direct invites.
Dark Souls had a very interesting concept for co-op. The combat was punishingly hard in that game for many people, but the player always had the option to lay down a summoning circle that would automatically draft other players of a similar level who wanted to engage in the co-op to help fight, especially with some of the game's bosses. The host player would receive help in a hard section of the game, while the joining player would receive bonuses and rewards if they were successful. In addition, there was a way for players to "invade" the games of others, triggering a PvP match.
While I do think the PvP model is rather annoying, I did really like the co-op option.
I believe for DA, which emphasizes story and character roleplay so much, including a group input on conversation would just lead to frustration and derision. In fact, standing around watching other people talk would be quite boring for a lot of players, even friends. So I believe the "instance summong" co-op of Dark Souls would be appropriate.
Keeping with my non-combat skills streak of the last MP idea, I believe this should play a role here as well. How about if, during the SP campaign, there were numerous dungeons/areas that required a member of the party to go off and do something that makes them unable to engage in combat. Think like ME2's suicide mission, with a team member in the vents, disabling computers, or a biotic squad mate providing a shield against the seeker swarms. Except, instead of ME2, which just used an unoccupied team member for this task, the game used a member of your active party. Essentially, you would be down a man (or woman) for this area for combat.
BUT, instead, at the party selection screen, an online player could ask for help. This would draft another human player to join the host. This could be done in one of two ways - one, where the joining player helps out with combat, or two, where the joining player takes the spot of the "lost" party member, allowing the joining player to engage in the non-combat tasks, such as activating runes to open a portal while enemies pour in, or picking a particularly difficult ancient lock.
The non-combat work for the joining member interests me most, so I'll just go with that now. What is the fun in just standing around, watching a bar fill up while the host and his party get to engage in the combat? This is where I figured some type of mini-game or activity involving the said non-combat skill would be enjoyable/entertaining. Perhaps something similar to the Bethesda lockpicking, or maybe even the Quest for Glory 5 trap disarm, where you had to perform a type of Memory mini-game (haven't plugged QFG these past two weeks now). Perhaps some type of geometric pattern or puzzle for a mage to disable a ward.
Whatever the case may be, these could engage the joining player in an activity instead of just standing around, watching all the "fun" happening. Also, if the joinign player isn't protected well by the host, they can get wacked by an enemy, which would interrupt the mini-game and possibly kill the joining player.
This will give the host player an extra hand in fighting by getting their full party back and would, in addition, allow them to get past obstacles faster if the joining player is quick at the mini-games (although it could also take longer than the computer if the joining player is fairly terrible at them). The joining player would gain rewards for doing co-op missions, in terms of exclusive gear, more money, extra XP, perhaps even MP related kits, if we were to combine this with the previous idea I had for MP.
It would not result in the host player "losing" control of any of the members of his party to friends or strangers, but would rather actually return a companion that would have been otherwise occupied. Similarly, it lets players who want to unlock loot and even possibly grind for more XP if they find they are stuck in a bind by going back and helping hosts with earlier areas/encounters. Maybe the rewards can even include special potions/tomes that give permanent stat boosts, or allow for a reset of a build (like the Maker's Sigh in DA2).
Thoughts? Questions? Feedback?