I am actually starting to find Mega Man not as likely as I did.
I mean, as stated, Sonic had a huge following for him; he was from what I understand, the most wanted character for Brawl worldwide (though most of his support came from the West, as Sakurai said). Mega Man? While possibly the most wanted 3rd Party, is far from the most wanted character in general. He's still got people like Ridley ahead of him, as well as Mewtwo and Roy, cut veterans.
And even then, Sonic wasn't even added into Brawl until 2007. Think about it; had Sonic not been so demanded, we would've only had Snake as a 3rd Party.
So what does this mean for Mega Man? That unless he "steps it up"
, and becomes the top character for Smash 4, he might not make it. Heck, we might not get any new 3rd Party, and just keep Snake and Sonic as is.
And then there's the fact that Capcom pretty much said that it's up to Nintendo/Sakurai, which means that they aren't going to put in the effort to have him included.