The game is really nice !
My thing when I play a game is having some kind of goal (other than just finishing it) while I play, like unlocking costumes, colors, playable characters, artworks, etc.
It gives some extra motivation to keep playing.
Here, I could totally see something like unlocking characters colors between each run (using some kind of resource or currency), to motivate players to complete the game.
Or maybe a gallery with artworks, like the one on the ending screen
My ultimate kink is costumes, but I know that’s a lot (probably too much) work ^^’