Well, first of all, I'd like to back Ice and say that Evolution was a good animated cartoon. Yes, it was padded and fluffed for the little kids, but there was a story that probably went over their heads. They introduced a lot of X-Men characters and they proved true to their actual counterparts in the comics. The plots may have been the shows own but to see what they did was very refreshing, especially with Apocolypse. If they had continued the show it would have been stupid because the way they ended it was perfect. They didn't cancel it, XTF, they ended it with the last few episodes, leaving the story open ended, which I thought was a good way to leave it.
Second of all the Ultimate Mutant Massacre already took place. Sinister slaughtering the four mutants was the Daily Bugle's idea of a massacre. Although it would be cool to see the Ultimate interpretation of the Maruaders, I don't think we'll get a chance anytime soon unless they elaborate more on Sinister and a possible following... He seemed to preach about evolution, which could be something that could influence mutants into backing him. I think that would be the most interesting take on his character and theirs.
Lastly, the four Horseman were speculated to be the four that Sinister actually killed. That would be (well, thought to be, anyway) Marrow, Synch, Maggot, and Siren. Who knows, though? That's what the fans came up with, not Vaughan.
Anyway, I said "no" because I don't think Vaughan intends to take Apocolypse any further.