I think that would be actually a good story, that the Darkspawn where accidentally or on purpose made by the chantry. Also i hope that if they do another fade section it will be more interesting, while i liked the idea of it in the first game i thought that it wasn't protrayed that well, Reminded me of the Hell level in Doom 3, brillant idea not that well executed. Also would be cool to see one of the old gods awaken without being corrupted.
Personally i think the storyline shouldn't be the normal "end of the world as we know it and your the only one who can stop it" A lot of RPGS do this and companies struggle with the resolve. If it is scaled down a bit, or altered so that the fate of the world doesn't rest on one man/woman's shoulders would make it more interesting.
I am interested to see if past companions come back as companions, although i am pretty certain Lelianna will be one, along with Cassandra. As both are searching for Hawke and Warden and both of those characters we are told will appear as NPCS. Still i wonder how they will do the Warden as they are trying to work it so you don't need your old saves. Yes there is a default Hawke but was there a default Warden???
Also i would like it if they reintroduced dual wielding swords for the warrior class. Also i think Bioware need to focus on the RPG element and not the action, as they admitted they dumbed down the RPG in DA2 to make it more accessible to casual players, wether this was Bioware or EA's idea i think it was bad one, and i hoped that they learned from that error.