I kind of ascribed to the Mafia A and B theory myself. Working from the lore Onyxia works for her father Nealtharion aka Deathwing. This would still leave her brother as an option, and all three have had human disguises to boot. The "Prestor" family would work well as a mafia faction that could be a variety of sizes really, but would logically cap at 3 which would leave 6 total mafia as someone stated earlier as possible.
What ties it together is Kel Thuzad being evil. Admittedly this is an assumption, but prof has responded to my theory and not debunked it. Assuming, for the moment, this means his character and alignment match up (a google search would show it) then that makes 4. This would be the more Lich King faction, or possible Burning Legion as that is where the power chain ultimately leads. This could again be as big or small as possible, but 2-3 would make the most sense.
Anyone who wants to debunk this can really. Of course I would view that with a certain level of suspicion, but if no one comes out to back my theory then perhaps it is all off base. My disgusting knowledge of Warcraft lore will either prove a weird distraction, or a really unexpected twist for Linkz.