Re: topics.
1. I'm expecting some info dump about Grey Wardens from the incoming novel "Last Flight". It was rather disappointing for me, that despite GW being the central theme of DAO we know so little about them. We had very little time with Duncan, and Alistair knew not much more then our Warden (useless rookie!).
2. One of the trailers shows Inquisition attacking GW Fortress (possible? unavoidable?). We'll be dealing with them, that's for sure. Allies or enemies, we should know more about them.
3. The leak
4. Both Flemeth and Morrigan talk about staying on the precipice of change. Something big is brewing. Thedas is going on the wild ride. Mages, Templars, Andrastian Chantry, Old Gods, darkspawn, Grey Wardens - who knows? (Well, BioWare does, obviously)
So, obviously, Blackwall will be involved in all these big events and he will have his own story arc (they all do). Maybe he will reassess his values a lot. So they can do a lot with him. Concentrating on the Calling - well, for me, sounds like an overkill. That doesn't mean the Calling will not be part of his story. I just hope it will not be the cental, main part.