4th SC2 Race?

What do you suppose it'll be?

The Xel'naga? or the Protoss-Zerg Hybrids?

My take on this is that it'll initially be the Hybrids, let loose as the ultimate threat to the Koprulu Sector, maybe eventually the entire Galaxy, and near the end of final SC2 installment, the Xel'naga themselves will make an appearance to help get rid of the Hybrids and maybe the Zerg as well, to correct their mistakes.

Either way, a 4th race would very likely be implemented as the Naga were in The Frozen Throne; maybe you could control some Hybrid units duringHeart of the Swarm, and some Xel'naga units in Legacy of the Void.