Musically, what I would absolutely love is if they took minor inspiration from Allstar Rumble when remixing/orchestrating it.
These
two songs explored the use of very digital/chiptune sounds, alongside more normal instrumentation, to great thematic success. Were such a thing applied by somebody with more experience (and, quite frankly, interest) than those working on Allstar Rumble to music from the franchise that was already of great quality, I feel like the results could be truly stunning.
Forget the actual music from that game, though. Like everything else, it wasn't great.
My favourite thing about Allstar, to this day, was the broken ukemi system where you could flip upright with a button press just before landing, even if you were already upright and even if you were about to land from such a flip. You literally never had to touch the ground, though it was hard to pull off on non-flat terrain.