I don't believe such subraces exist in WoW, and doing it along those lines would be ridiculous since Arathor is the wellspring of many of the later nations. We're not talking about huge time frames here, either, nor are there evolutionary "steroids" available to the humans like the Well; the Curse of Flesh had already run its course by this point, too. Plus, these regions are all broadly similar in their climate, with Stormwind being more temperate and Lordaeron colder; IRL, and in games like TES, you have a broad variety of climates and other evolutionary pressures combining to give different races or whatever you wish to call them. You could do what Blizzard did with Gilneans, and limit the appearance options for each subrace and subtly change some features, and even give different subrace perks, but why re-write their lore entirely for an auxilliary feature?