Dwarves, gnomes, and many other fantasy races don’t exist within Sanctuary, so I honestly don’t see why anyone would be able to suddenly play as them.
The best you could hope for imo, is for Diablo 4 to have a powerful character creation feature that’ll allow you to make a multitude of adjustments to your character’s height, body shape, ears, and whatnot (I wouldn’t count on that though). Beyond that, I have to say to anyone wanting to play races outside of humans/nephalems; you’re out of luck.