As happy as some people would be what would YOUR reaction be to Goku coming to Smash?
I'm a Dragon Ball fan and a Smash Bros. fan. I strongly believe those two franchises should never interact. Smash is and has always been about video games. To extend the scope would make it lost its essence in my eyes.
"Ah but you forget that in the beginning, it was only Nintendo characters, and even Nintendo protagonists. Melee introduced bad guys and Brawl introduced 3rd parties, so extending Smash to manga and anime is exactly the same."
It is not, not at all. Lets say you are watching a series about some guy who moved in another city. In the second, he moved in another state. And in the third one, he goes to another continent. Would you say that the next logical step for the show is to bring him to another planet?
"But Sakurai wanted James Bond, so non video games characters are totally legit."
First, the fact that he thought about it doesn't mean that he would have stick to it. And second, what is or is not inside the creator's mind doesn't affect the final product once it's released. Maybe Sakurai wanted Smash Bros. to be this or that, but in the end, Smash Bros. is what it is, no more no less.