Have you ever wondered that how Equestria's continent was born? What if Equestria was once one massive landmass. Until landmass had been blasted apart from a main land by some a massive magical catastrophe? Perhaps ruled by a ancient alicorn society. ( reference to The Highbornes. ) Ruled over a regular ponies.
And young Celestia & Luna were part of this race. ( reference to Malfurion & Illidan. Luna will become corrupted by jealousy and turned into demonic Nightmare Moon. Similar way how Illidan became Demon Hunter. ) Which explain why there is no Alicorns in Equestria, until Celestia grant that power to Cadance & Twilight.

I think story goes similar path with The Burning Legion invade and is pushed back by natives and powerful beings. Causing Equestria's landmass blasted apart from a main land. Lead to Celestia & Luna to form the Equestria kingdom. Away from their ancestor's mistakes.