how about a very late-game race mix E.G. ability to buy/reverse engineer other race's workshops (obviously allied race workshops will be easier to peacefully acquire than enemy ones).
You'd think a citadel of dwarven/human/warlock/etc opulence would at least try to mimic the successes of the other races.
This would kind of diminish the specialness of humans being able to have the merchant stall from any race. Without that it's kinda just guilds and the 8 blocks from a rock, and guilds are kinda hardmode for humans anyway as I understand it (I have only played one human game and I erred badly very early), dwarves have them faster and easier.