The walls for who gets into Smash Bros keeps getting lower.
Super Smash Bros (Only Nintendo All-Stars)
Super Smash Bros Melee (Only Nintendo Characters )
Super Smash Bros Brawl(Only Characters that appeared on Nintendo consoles)
Super Smash Bros 4 (Any Video game character)
Super Smash Bros Ultimate (Any character that appeared on a video game?)
I wouldn't be surprised if Goku is in the game to be honest. After Cloud got in I realized that there are no rules. If there are rules then they WILL eventually get broken. Smash Bros characters are like a slippery slope now.