Assuming a new class is introduced, I hope it's not going to be a Demon Hunter.
Why? A demon hunter is extremely cool but the problem with this is that well, gameplay and mechanics wise, how are they going to be any definite from a warlock or rogue? The spells they use are all Warlock spells, the dual weilding rogue style, demonic forms, I don't see a gameplay reason to add them. Lore wise, yes, definitely, but gameplay? No, I can't see it.
More gameplay reasons is well, every new class so far has been a melee and a tank. We did get monk healers yes but it would be silly for Blizzard's next move to not include a healer - or at least a ranged caster. They definitely will not introduce a pure class however, mechanics reasons are obvious.
Yeah just my thoughts, what do you all think?