I'd love that, since I already have 8 90s and leveling 9 one.
But. I'm highly doubted that Blizz would implement something like this. Remember tons of whineposts about "being forced to lvlup opposite faction char"?
Imagine the shitstorm about "bad, bad Blizzard forcing them to lvlup while they don't want to, but they are forced to do that awful routine over and over because they feel it's now mandatory". Oh, that mindless gamers generation nowadays... lol.