I don't see Nightborne Demon Hunters. At all.
Look at the Demon Hunter quests, now remember that the Nightborne can only leave Suramar without sources of Arcane Magic and not wither because of the Arcandor.
Now there are two races I could see getting Hero Classes: Dark Iron Dwarves and Void Elves. Dark Iron Dwarves have been around longer than the Scourge so they could easily have been taken in as Death Knights. Void Elves on the other hand could potentially be given Demon Hunters or Death Knights, they literally just need to have taken on their Void aspects AFTER they became what they are — which they could easily hand wave in the questlines.
For everyone else? Not really a lot of options. Maybe Zandalari Trolls could potentially be DKs but that's a giant stretch to actually make happen