Agreed, I think Nelf paladins make a ton of sense and really should have been added way back, even before legion. They also have a deity they worship which makes it pretty easy to associate some paladin lore with them, similar to what they did with Taurens and Zandalari, but they can do it in a very good way with nelfs.
I also want to see orcs get a nice off group of paladins, they have a sect of priests and they are also a very devoted race. It can work well if done properly.