So we know that when dragons breath fire they are performing a dragon shout (saying certain words in dragon language). http://www.youtube.com/watch?v=yMjdvB5AwbY&feature=player_detailpage#t=66s for example the dragon says something along the lines of "TO SHA" and breathes fire. Will there be restrictions on dragon's dragon shouts capabilities? Can't a Frost Dragon shout "TO SHA" and still breathes fire instead of frost or a Fire Dragon breathes frost by saying the same shout a Frost Dragon shouts when breathing frost? Discuss.

I think there will be some restrictions on what shouts the Dragons can use in-game, but in lore they will be able to use all.

My guess is that dragons will, generally speaking at least, only have access to certain shouts. I seriously doubt we'll see "fire dragons" using the frost shout, but they may have access to more than just the one for fire (like the knockback, for instance).