Hasn't it been on the record multiple times that they don't want to just throw in guest characters willy nilly because that would detract from what Smash Brothers is about?
More likely than not, Protoman will just be an alt. color for him (If you're lucky, they might pull a Wario and give him a texture swap into Protoman, too).
X is unlikely because they went with the Super Deformed style Megaman, while X had more accurate proportions.

Anyway, I was about to decry Megaman as "Samus with a slide kick"
Then I saw the trailer. My jaw hit the floor. Thank god Metal Man's power was included. I love that one. A bit saddened that MM doesn't change color, but considering the nature of Smash Bros, I guess having a 4 person Megaman fight with everyone swapping colors would be confusing as all hell.

Okay, this game has convinced me…I NEED a Wii U at some point now:

http://www.youtube.com/watch?v=APWTJMyM4qg

This is a funny character announcement :lol
https://www.youtube.com/watch?v=rqxDPJmO6f8

Smash Bros :D!!!!!

Officially buying a Wii U AND a PS4 now :lol

Hm...the robot designs do certainly look interesting.

It's a new Xeno game.

That's all I need to know.

Oh, really? Hm...

X isn't that unlikely. They had Wind Waker Link and "Regular" Link at the same time before.

From that point, fair enough.
X is still unlikely from actual inclusion, though.