I think that Alistair's dragon's blood/Darkspawn taint interaction might possibly be a moot point, when you consider events from DAO: Awakening and DAII.
In DAO: Awakening, The Architect found a way to quell the call of the Old Gods to the darkspawn. The Broodmother describes it as singing; she resents the Architect for preventing her from hearing that beautiful song.
In DAII, Bartrand goes mad after being exposed to the Old God idol made of pure lyrium; he describes hearing beautiful music, which to me was suspiciously similar to what the Broodmother describes. Varric starts exhibiting signs of madness, including hearing things, in the quest "Haunted", just because a shard of the idol is still present in Bartrand's house. Meredith also goes insane from exposure to the idol. Basically, it was turning humans, dwarves, etc. into something pretty much like Darkspawn.
When speaking with Nathaniel Howe in DAII, we learn that the Grey Wardens are working with some strange allies. The strong implication is that it's the Architect and his sane Darkspawn. It is entirely possible that The Architect and the Grey Wardens are together working towards a cure for the Darkspawn taint based on the Architect's work with Darkspawn and what Hawke et al discover in the primeval thaig. If your Hawke spares Bartrand's life, they have Bartrand to test things on since he goes to an insane asylum. If not, there are still a lot of Grey Wardens who might willingly undergo tests for a possible cure so that they will never experience the Calling. In which case, Alistair could be cured of his Grey Wardeness, as could the Hero of Ferelden if s/he survived in your games. Then, Alistair would be back to having dragon's blood and no Darkspawn taint, so the chance of him becoming a big baddy is small.
Since The Architect needs Grey Warden blood for his cure for the Darkspawn, it is in his best interests to cooperate with the Grey Wardens and that might include being asked to investigate a cure for those who have survived Grey Warden initiation.
Finding a cure for having undergone the Grey Warden initiation could be an important priority from the Ferelden crown's point of view, so that Alistair has a better chance of siring heirs. Also, if The Architect's work is successful, then there won't be any more Blights, so the First Warden might want to look into cures so that all the Wardens under his command don't suffer meaningless deaths when they succumb to the Calling. This nicely explains why a cure would be pursued even if Alistair doesn't become King in your games.
Supposing Alistair is cured of his Darkspawn taint, his dragon's blood might yet mean he has an important destiny to fulfill. It might not be an evil one, though.
Modifié par ladyiolanthe, 23 juin 2013 - 12:28 .