One thing to note is that Sony creates new ips all the time. Nintendo unfortunately doesn't. I was actually having a hard time thinking of Nintendo characters that could be added to smash that people would actually care about
SuperBot can also create a few new characters if they wanted to, then there are the allstars in the future. That could mean people like Jodie Holmes and Aiden and/or literally characters announced and shown for the first time in PSASBR.(Which just sounds awesome!)
I see this game having a sequel on the PS4. The original Smash Bros was mediocre and it received 2 very good sequels (by mediocre, i am speaking more about the amount of content in the game). So why not this? Even if this game was mediocre, it could very well get a sequel.