Just finished reading the 'Sera as a goddess' theory. I'll give it this much- if that turns out to be the case then it means this was very carefully planned in advance and executed with great subtlety.
As for the next game, I think it's highly unlikely we'll see a complete departure from previous characters. I mean, as the series currently stands you can essentially play six degrees of Kevin Bacon with any DA character of note and connect them to anyone else. It seems almost certain that we'll have returning characters in support roles and possibly one or two as party members.
I do however agree that I'd like to see a new locale the next time around. I think Antiva has a lot of potential. (There may well be books or other fiction already set there but I'm only familiar with the games.)