I like this idea in theory, but I think implementing it might cause more problems than it solves. In addition to what Jeff saidJeff said, you'd need some sort of migration notice for "answer questions."
Including a migration notice defeats the purpose of reducing clutter and noise, although it does help with logical organization and solves the problem of questions being unanswerable due to being posted in the wrong place.
Not including a migration notice is no good because the asker of the "answer question" probably wouldn't understand what happened. (Neither would anyone else other than the migrator, for that matter.) In addition to this not being helpful for anyone, it would lead to a number of possible bad reactions:
- asker re-posts the "answer question"
- asker posts as a real question which is then obviously a dupe
- asker gets frustrated and leaves, spreading the word that SO sucks
- &c.