I hear fans say "this guy should be champion not Roman Reigns" all the time, just saying.. The question is would Namco think Goku would be best for business considering the success of Fighter Z? Never say never.
Actually, if anything, Goku's recent success in FighterZ and upcoming major appearance in Jump Force would likely
hurt the chances of his publishers wanting to put him in Smash. There's such a thing as diluting your product.
You can play as Goku in Xenoverse? Awesome!!!
You can play as Goku in FighterZ? AWESOME!!
You can play as Goku in Jump Force? Awesome.
You can play as Goku in Smash Bros.? Awesome?
I realize that Ryu is in every Capcom fighter, but the Street Fighter side of Capcom vs. ______ isn't exactly the fan service that gets people excited. Goku is different. He sells **** on his appearance alone. You don't want to over-saturate the market with guest appearances and lose the unique appeal of announcing him in your own products.