i believe the youtube app uses 7.x keys, so it wouldn't really solve that...unless it does turn out to work with 7.xthere is a huge gain in updating to 6.3, as most likely, a kernel exploit will be found (not sure if one will ever be released) for it sometime later on. the huge gain is the 6.X keys. that would fix youtube and the 6.x saves. that would allow pokemon carts to be used between updated consoles and the 6.3 one without wiping the save every time.
it would solve the 6.x save issues though, but once again only for people who haven't already started their games using the 4.x keys in emunand....plus it would likely make everyone saves incompatible...unless its patched to detect the save keys used and switch as appropriate