Something I've been wondering and can't even remember asking before yet have the slightest feeling I have...What gives Terra the authority to "choose" a wielder? Just cause his emblem is gold?
Yes. I did use KHwiki. I really gotta stop using it, because it's a load of crap, but it makes me feel smart to cite it.
Trying to contribute, in regards to the quote above, I would say that's some of it. I think that he chooses Riku towards the end of the game, after he's progressed through aprrenticeship, maybe not to the point of master (Because I think he morphs/whatever to Xehanort before that), but where he can perhaps assess that Riku has a strong enough heart to become a wielder.
And I think it would just be wrong for MTAV to tell TAV who the next wielders would be, assuming that they would be the apprentices of TAV. Perhaps he would have a better judgement, but I still think it would be up to whoever the wielder is.