DeuceBlade makes a valid point, Bowser and Bowser Junior are nearly two different characters that are related, much like how Diddy and DK are related, if I'm not mistaken. Or another example is Mario and Luigi. Sure, there's more Mario games, making his moves more unique, but Luigi has evolved throughout his career. When comparing his gameplay in SSB and SSBM, he was less of a clone of Mario and more of a seperate character.l
Bowser Junior would be a middle-weight, even if he is smaller than Bowser, which should make him lighter. He is nearly Mario's height though, and with his hard bony shell, he would be considerably heavier. He would use his paint brush, I would hope, to extend his reach about equal to Bowser's reach when he's at regular size. He could use his brush to create a gust of wind as his Up-B, mush like when you had to chase Shadow Mario through Pianta Village.
He has more potential than Geno, even if Geno has more fans. He has been in more games than Geno, I'm guessing around 10 now, compared to Geno's 1 role and 1 guest appearance. Bowser Junior is all around a good character, and may, hopefully, be an unlockable, much like Pichu was unlockable in Melee.