They would be dumb to not make more. The next game will most likely have the same amount of characters as Brawl, if not more.
I would expect there to be double the amount of characters than in Brawl. This is the next generation, there should be way more content.
On the related subject, I'm super pumped for classic Mega Man in the latest Super Smash Bros. Mario Kart 8 looks interesting but they need to show more of it for me to get
really excited for it. The latest main Mario game feels a bit lacking on the "wow" factor but I'm glad you can finally play with 4 people at the same time. Also allowing you to play as Peach is a nice touch.