According to a poll on the Capcom Unity forums, Mega Man X is the most wanted DLC character for Marvel vs. Capcom 3. He ranked in at a whopping 34%, beating out other notable characters like Strider Hiryu and Phoenix Wright. I am all for his inclusion, and hope Capcom listens to the fans. He is the only cool Mega Man to not be featured in a crossover title as the original Mega Man and Rockman Volnutt have both been previously included in Marvel vs. Capcom and Tatsunoko vs. Capcom.
A few people have complained that Mega Man X is too similar to the original Mega Man, but they don't seem to be aware of Mega Man X's abilities. Mega Man X gains the Hadouken and Shoryuken in X1 and X2, which makes him sort of like a robot version of Ken. X also gets different armors that allow him to do things like fly, gain stronger defense, and upgrade the buster shot. Another cool thing is the mecha suit that X can pilot makes him sort of like Tron Bonne.
Mega Man X deserves his time to shine. Make it happen and you will take my money, Capcom!