Hmm, Im not sure, considering we have no idea what the protoss will be doing at this point. It is possible they could setup a 4th title to combine the 3 races and have them each doing missions to work on stopping the big bad. But it is also equally likely the protoss game will be them uniting with the terran and zerg with the final mission being that vision of doom from WoL. Considering the ending of this game, its got a solid chance of happening that way instead of a 4th.