Given how they played a quite peripheric role in they very Old God expansion they were introduced for, it's unlikely they will ever have a major role ever. As for NB, they also had a very reduced presence in BfA, but the huge role they had during Legion more than makes up for it. Blizzard doesn't care about writing for any playable race outside human/nelfs in the Alliance and orcs (and maaaaaybe forsaken) in the Horde.
The Nightborne's story was far more fleshed out, though I don't care for the player character models much.
I will also say, I think Nightborne should have been a neutral Allied Race - both sides helped them extensively. This was silly of Blizz to feel like if Alliance gets one, Horde gets one, vice versa. Sometimes I honestly wish the factions weren't so perfectly mirrored. It's not realistic. I understand WHY, but come on...