I understand they start at 98 and after questing it should be 100 if im not mistaken? I know that DK's required you to have a higher level character.
I am cautiously optimistic about this expansion, looking forward to the Warlock and Priest changes. Not sure what to make of the rogue. I kinda wanted them to do advanced classes. So after you get to 100 any class that gets to that point would have a quest line for example to turn their classes into something more advanced with new abilities, looks and even play styles etc.