I doubt Nintendo would actually go for it, but I had the idea that if Master Hand was just some kid playing with his toys, what happens if the kid grows up? They need to work a job, they don't have time to play anymore, and eventually the trophies go forgotten. Years later, "Master Hand" rummages through a bunch of his old stuff and finds all his old figures lying around. He brings them out just like old times, but the creative spark has faded. it's just not the same. His child takes interest in the toys, though, so he leaves them out for her.
Skip forward a bit, we find the child hasn't really been playing with the toys either... But she does use them as an art reference, keeping the creative spirit alive in a new way. This also facilitates a soft reboot, with a more stylized art style and a new "Master" boss. I guess that would be, like, Master Artist? Master Pencil? We should definitely keep the Hands as around as hidden bonus boss, of course, just not center stage like they used to be.
...Yeah, when you lay it out like that it does sound a bit fanfic-y, doesn't it. I thought it was cool, at least