A few ideas...

[RebatemanYT]

Idea 1: Custom Ranking Goals
So basically, you know how 60 points means OK and 80 means superb? What if we could change that ourselves so, for example, in harder levels we can have it easier to get an OK and on easier ones, Superbs are harder to get? Maybe even custom rankings counts, graphics and SFX/music. For example, you could have Try Again be at 1 to 59 so that if you do nothing (getting a 0), you could achieve an "AFK" rank.

Idea 2: Custom SFX
Similar to in RHRE3 where you can add your own SFX for your own games, what if there was an option to change the SFX for various things? For example, fart sounds when widgets explode, etc. You could either have this as per-level or player by player. Or both, with force priority being toggled on and off in the game options for the player by player one.

Idea 3: Universal Custom Pallets/Textures
Some people can't see greens or reds easily. Those are default colors. So why not have the option to change what the color pallet you force on yourself in the options alongside toggling it on and off? Also, same for custom texture packs.

Idea 4: Multiple Custom Textures In A Single Level
Let's say you want to make a level based on a mashup that has many themes like, let's say it transitions from lego to circles to triangles. Well, if you want all of those textures in one level, too bad. But why does it have to be this way?

Idea 5: Specific Arrow Blocks
Tired of your players just using the D and J keys if on default controls? Want to spice up the gameplay of your levels? Wanna recreate more accurately Guitar Hero maps in Polyrhythm Mania? Well, if this happens, all that and more could happen! And how will you tell if it's different? The + sign on the + blocks would have more alternates that, by default, would all have the arrows you can't press have the inside color of the blocks. But with custom textures, you could change it.

Idea 6: Change The Block (and text) Color Pallet With The Color Pallet
You know how you can't change the block and text colors (the white) in the game? Why is that? I can't have a proper fade to black without wasting my only custom textures slot.

Idea 7: Change Specific Textures
This would go hand in hand with the multiple custom textures idea. This idea would allow you to let's say go from both + and A being circles to A being circles and + being HD when extended but GBA when unextended, then HD on both extended and unextended + in the middle of it. All by just toggling to change those textures.

Ideas 8 and 9: Secondary Keybinds and Mouse Keybinds
What if you could have both WASD and arrow keys at the same time be d-pad? What if you could have both D and left-click be d-pad right (or A and left-click) while J and right-click is A so you don't have to have to swap keybinds in the options if one is getting too boring for you or whatever.

Idea 10: Multiplayer
This feature could be changed in the level metadata so that level is either split-screen only (with max player count being up to 4, set by the creator) with different inputs for each player similar to Karate Man Wii, take turns for up to 4 again similar to Ninja or Sneaky Spirits 2P in Tengoku Arcade, Megamix styled (can be either split-screen or online if possible, maybe LAN or Steam if Steam is OK with it being on there (after all, look at Crab Game's steam trailer), with everyone only seeing their screen) with everyone always getting the same inputs on each screen. You can also disable all multiplayer or enable specific ones or swap mid-game between them or force multiplayer or even...

Idea 11: Alternative Maps
You could have alternative mappings as an option so if they want, without having a whole bunch of mapping files, have different difficulty or multiplayer or the split d-pad idea versions.

Idea 12: Sub-Folders
This will simplify mashup album in polyrhythm mania organization. Still, if you want to have a folder for let's say your already played levels and your yet to stream levels for streamers or for mashups vs single tracks or stream safe vs dmca stuff, you could just put them in sub folders and, with this idea, navigate through them without changing your default directory every time. You could also potentially add shortcut support so you can have let's say mashups folder with mashup albums folder within, but an albums folder with a shortcut to the mashup albums folder within. Also, speaking of organization...

Idea 13: Track Numbers (and other organization tools)
This would greatly help with albums or listing orders for streaming. Maybe you could have even a reorganize feature where you can have a folder of maybe shortcuts to tracks be all in an order saved in a file added to the folder if you save any organizations. Also, track numbers would be optional metadata so if you don't care or aren't doing an album, it isn't needed. Also, by default, the non-numbered ones would be at the bottom of the list, but reorganizing them would mean that you could change it.

Ideas 14 and 15: Last Played and Score Nicknames Or Profiles
Simple idea. Just add a metadata where it shows the last time that copy was played (which can be edited by playing), by who and the score they got. Also, this would benefit from adding like high score or actual score nicknames OR adding profiles so that different profiles for different keybinds, scores, textures, pallets, and more.

And that's just some ideas I have. Some I think would be unreasonable like multiplayer, but 12 and 13 I think should happen. You don't want to get your levels mixed up for if played on stream or not as well as order of tracks in an album.