Nightbourne doesn't really step on Night Elf toes. Void Elves were given an inch and eventually stretched it into a mile - High Elves are now functionally a neutral race. If there was a race that the Horde could import to the degree that Void Elves "borrowed" from the Blood Elves... again, I'll take Draenei.
But yeah, Humans should never have free reign to strut around Orgrimmar. The argument can be made from a lore perspective, but as you point out, it is a betrayal of the core of the franchise. If faction lines are softened, however, I wouldn't mind seeing Alteraci as an independent or "neutral" race.