Honestly, as I think about things I wish were in KS, one thing that comes to mind is more enemies which change in some way when the player has a powerup - like Bouncer #4, whose jump height increases when the player has a double jump. Being able to control the intervals at which certain enemies fire their projectiles would also be nice - I've never been very fond of the random element present in so many of KS's enemies.
Also, I just found a bizarre glitch. It's hard to reproduce, but essentially, by maneuvering between two screens and the screen loading taking a certain amount of time, I'm able to collect things on the exact opposite side of the screen.