Is there an existing franchise that you would like to see made in the vein of Mario RPG/Paper Mario? A recent example of that style is South Park and the Stick of Truth.
If I am going to pick another Nintendo franchise to be made into an RPG, I would pick Kirby. I think they would think of creative and lighthearted way to pick fun of RPG tropes (The RPG inspired boss battles in Kirby Super Star come to mind as a very minor example).
As for something random? Star Trek. Of course it would be a far more serious game in tone and style, but I think the right developer could make it work. Doesn't matter if it is based off one of the shows or is simply set in the Star Trek universe.
Your picks?