I don’t think we’ll ever see a new standard class added to World of Warcraft again. Legion comes with both a Level 100 Boost and Demon Hunters start at ~100. You can start Warcraft fresh, on a new account and begin play with two level 100 characters.
Once we are leveling from level 110 to ??? asking someone to level from 1 to (lets say) 120 won’t really be expected anymore. People will either race change or boost their characters. When you consider that most people want to play end game. It’s just another barrier to entry for people to have to spend X amount of time putting in leg work to get a character up to where they can participate in the fun new exciting aspects of an expansion.
Honestly thought, It might be time that ALL new characters start at level 40, or 60, or 80 (perhaps new characters start at the max level of the latest ‘free’/bundled expansion). I don’t know how much work that would be to do, if it would even be possible to do at all. But I think it would be a boon to the game.
It could even be done one or two classes at a time. An expansion that focus heavily on an existing class could ‘upgrade’ that class to a hero class. Give it another spec, open it up to all races and start it at level 100.