I'd assume that all the information needed is there [if it's anything like Oblivion, this would mean nodes, animations, etc are already tweaked for us - there seems to be a mounting animation, entry point, etc]. Flight also seems to already be in the game, so it won't have to be done from scratch like in Oblivion [anyone remeber the Akatosh mounts?] I'm rambling, but point is, it'd be easier to do than from scratch, so a mod like this is bound to come out in the near future [relative to the release of the CS, of course].