Not sure about the orcs, but highmountain, nightborne, void elf and lightforged draenei have some validity mostly due to the fact that what was datamined is that for some reason they can equip armor, which obviously no NPC can do that, it's a player only thing.
I am hoping there's subraces for everyone though. There's a ton of different cultures and lore (and badass tattoos), and it honestly wouldn't really take that much work if they're just reskins which I find to be the most likely if they ever did. You're just retexturing something instead of designing new races that require an update on every single item available in the game for them to be able to wear, etc
It's possible, but the NPCs are not "wearing" anything, their entire model is built like that as in their gloves are a part of their body, you can't remove them etc. Which is why you can have some mobs that are insanely detailed vs player gear which is mostly just texture work until very recently with adding like beefier plate boots, etc
