I would love playable goblins, though I do feel we should get all the core races in first. We're missing gnomes, half-orcs, and dragonborn. Which is a big shame for me because half-orcs and dragonborn are my favorite core races.
Personally, I'm 100% sure that Larian will be brought in by the gnomes.
Even now, there are gnome characters (AND svirfneblins) in the game. I think we can play EA for them. In any case, it would be very strange not to introduce them.
It seems to me that the lack of half-orcs and dragonborn is due to the lack of a model for them. The dragon face is difficult to animate, and the half-orcs... Well, apparently the model for them has not been created yet. It seems that Blurg (Orog in Out of the Abyss) became a hobgoblin because of this.
I'd also argue we should get Githzerai as a priority option as well, as we already have Githyanki. Githzerai would just need different dialogue options and racial bonuses since they look almost identical to Githyanki.
Well, since the githzerai and githyanki are very similar in physical terms, Larian should have no problem creating their model.
It will be much more difficult to give the correct NPC reaction and dialogue options for the character. Imagine what a githyanki patrol can do when they see a githzerai.