In terms of popularity, Rayman finds himself in an awkward position.
On one hand, he's not as obscure as, say, Bayonetta. I mean, it's not like Rayman has to be in Smash to make his franchise more well known. He's iconic enough on his own, which is something other characters can't brag about.
But on the other hand, Rayman isn't a pop culture icon like Sonic is. Sure, he's well known among the gaming community, but outside of that, the mainstream aren't as familiar with Rayman as they are with Sonic. I mean, Japan has historically been a bad market for Rayman games sales wise.
Personally, I find that Rayman should be the last third party character they should add. He's one of the few gaming icons left that would fit perfectly in Smash. And you know what?
Rayman is a famous character. Even if the Big Four dwarf him in popularity, he's still an icon by himself. He is by no means a no name to the world of gaming.
I just hope Sakurai shares this sentiment.