Goblins already have models, so I would think they could be implemented pretty quick.
No, not in an immersive and believable way. You would have to change most dialogues, many quests (tieflings not letting you in at all...) etc.
Dream on, dreamers. I would be pleasantly surprised if even the non-mainstream races present in PHB are implemented well in this regard (except Drow maybe - fan service and thus money dictates Drow must be handled well).
