I hope I'm not repeating what already been said here, but...
While I like the bonus stages and was excited for them in the beginning, after many hours of gameplay I find them extremely boring.
They were fun at first, the transition from stage 1 to stage 2 was nice, but at some point you just memorize the tap pattern to the point of automation. I got so bored of them I actively try to dodge those portals 90% of the time and I have on several occasions closed the game because I accidentally bumped into them and didn't want to play them.
Hell, I wish i could get stage 1 instead of 2 again just for the sake of variety.
What I think would be cool (and I know it's a big ask) is implementing a rotation of different bonus stage variations. They don't even have to be drastically different, but just add some much needed variety. I generally like them as they are now, but I just think that it's a good idea to make it a rotation instead of one single bonus stage every time.
Thanks for taking your time to read this, and I completely understand if that's not possible for some reason. I just wanted to make a suggestion for a game I absolutely adore.