I am not sure how well I would believe some of these rumors. I mean, having a 6 inch screen on a controller is pretty interesting rumor, but how well would it be used practically versus the price of producing such a thing.
Nintendo has always been good at staying ahead of the market or in it by introducing interesting ideas. Motion controls is completely gimmicky, and I think the market's last 5 years sort of proves this. The sort of games that you get from motion control often ruin a game and it suitable for only a few situations. The main market for motion controls is the casual part which was untapped until nintendo showed up. However, there was always that hardcore crowd where video games really started, and majority of 3rd party developers prefer to make those kind of games. Nintendo has certainly learned its lesson, I believe, and will try to find a balance between the hardcore and casual audience.
Anyway, the next generation I expect would contain improved graphics. Playing games on something that does not feel new or upto date would not sell very well. This is the minimum I am willing to believe for next generation console from nintendo. The controls I expect should be a healthy balance between motion controls and regular. Nintendo seems to have experimented with that with the classic controller option, and they have 5 years worth of experience from the motion control.
tl;dr I expect the next smash game would run on higher graphics and suitable control scheme.
Now, if another smash game does come around, I think it would switch hands or would be a combined project between a number of developers. There seemed to be little interest to make another smash game. But, if another one does who up, it should probably be only in the discussion stages right now. Either way, it is still really early to think another one might be coming up.