Morlun, if he got some credibility back, could definitely head a Marvel wide event. Use the same premise as Absolute Carnage (i.e he is hunting all totem heroes) and boom, you can get something huge.
Aside from him? I honestly have a hard time. Venom is no longer a villain. Octopus could, but right now his villain status needs to be rebuilt. Green Goblin needs no mention. I think the Chameleon and Mysterio could come up with something elaborate. Some new tech or tricks could certainly amp Mysterio to Event villain, but he would need proper build up to that since right now he really doesn't have credibility.