I would love to see a true sequel on Switch 2 with new characters and new lore - give Mario some new friends once every 25 years!
Would be an innovative way for new characters/IP/stories to build out over time/generations.
That said, I'd love to see a sequel to SMRPG in a 3D style, rather than always using the "paper" style for RPGs.
It's very explicitly the successor of this game (also seen in how it kinda mimics some of the basic plot beats), it just got renamed during development.
Dealing with the disappointment of the new installments was one of the many things that ultimately weaned me off of regularly playing video games. I realized things didn't strictly get better, and that we often get sold things with just with a different coat of paint.
The badge system is phenomenally customizable. Different kinds of attacks, defenses, ways to play.