I doubt they would touch the major characters in DA1 or even DA2 (Even if it's a pretty new overall cast) in the movie. The most logical idea to get the story across while also showcasing the world and it's history is to give it a connecting prequel type feel to Dragon Age 2, instead focusing on the things leading up to the second game while keeping away from the major players as much as possible as to not screw any continuity. You never know though, they said they have a ton of plot made going forwards and backwards, we could easily get a Calenhad story as a '20 years later, the OGB...'. A tie-in set just a little before the game seems to make the most sense though.
I don't think they would touch any romances in it to try to give some sort of finality because they have to know that would fail. You would have to introduce characters with backstories, designs, voice actors, and what have you to play the parts of 'our' PCs, and you know the RPG fans will resist that when it comes to whomever they picked in game. Some wouldn't care (I can't say it would break my heart, but I'd rather have the story in game than film), but the more purist of RPG players would riot. In short, doing something like that would just appeal to the one and done crowd, not the six months and ten playthroughs later, and even though you want to make both happy and get both to spend money, Bioware has always catered to the more hardcore of RPGers while you had Blizzard for the click-boom crowd. (And I like Blizzard, but they are hardly deep most of the time.)
As to adding another element to Dragon Age 2, I suppose RTS would make the most sense. RTS/RPG goes together like Shooter/Mass Effect I suppose. I however would rather see the idea behind Vigil's Keep taken but done right. Instead of glaringly obvious choices (Here's iron, make armor. Here's silverite, make better armor. Here's gold, we have ridiculously awesome walls now), find materials and have to make choices that don't have a glaringly obvious 'right' answer. Find some ore? Do you want to outfit a select few elites, strengthen your run of the mill man-at-arms? Perhaps spread it out over the entire force giving even the lowliest archer a chain shirt? Have stone for walls? Well, you can thicken it with no frills so it can stand up to the toughest of bastilla and ram's, or maybe you get fancy and put in murder holes which give your archers some sort of damage reduction up on the walls, or add in spots for hotpots so you can basically drop mini-fireballs on the ground in front of the tar-of-death's placement. Even choices like space in your keep for what can go where. You want merchants, a chantry, a small circle outpost, spots for Blackstone, your soldiers wing, civilians, crops, storehouses, graneries, yadda yadda, you have limited room. Do you compress as much military as you can within the keep and stretch your defensible areas outside by putting farmers and shanties outside the main walls, or do you go smaller but more robust by keeping everything centralized and defensible? And then you get attacked and these decisions really shine or cause you a lot of damage.
Adding something like that doesn't seem any more difficult than adding RTS elements to the game, but I'm unsure how 'Dragon Age' it would feel.
I just want to see them add fleets and heavy cavalry to the next game. You look back around the timeframe the setting was birthed from, ships and horses were what people worried about. So I'd be perfectly happy with them adding in a 'mini-game' of mounted combat or ship to ship dealings and call it a day.
With all that said, perhaps this is what we'll get in the movie anyways...