I was wondering if there was anything in the lore that implies that demonic blood could empower any races other than orcs? And if not, what is it about orcs that makes them so susceptible to demonic taint? Does that imply some sort of common ancestry?
Right in World of Warcraft we see other races being empowered with demonic energy/blood. It's not just Orcs. Satyrs were once Night Elves (or Highborne, or Kaldorei), and I'm sure you've seen what happens to Blood Elves when they drink in the demon juice. The horned, winged elves you see in Magisters' Terrace, Sunwell Plateau, and the Throne of Kil'jaeden. They're not all specifically caused by drinking demon blood, but it's the same idea, really.