You mean Trolls are the backbone... Without trolls there's no Elves to make the several further mutations of the species.
Trolls are like the caveman and Elves the modern human I do agree. Another species of Elves isn't going to be ground-breaking nor would it be exactly a bad thing, I would however opt more for a class than another race personally but it most likely will be a race that comes next since Demon Hunter was the new class... If Voidy I would reckon Etherael a better candidate with visual changes considering the direction with Mac'acree.