Well, I'll reply with my own yapping : )
Ghost tapping
Thanks for the info! I think I'll just stick to ignoring the mispress since it's easier and this program is made for practice, not for score attacks.
Extra keys
Probably not possible. You might be wondering why, but charting in fnf (well original fnf) is very convoluted (and so is my code :3) so it'll probably be not possible to make it work across many mods.
Custom skins
Maybe! I mean if you look go to github link, there is a folder called assets, and there are image files that program can load on startup. If you copy that folder to where the program is and run it in terminal with
fnf-practice.exe -hot
program uses the images inside the folder instead of ones that are builtin. But that's a feature I made for myself and not for others.
Zoom on beat
Nope! Sounds like too much hassle : )
Including other mods
I'm not comfortable including other people's mod without asking (what if they get mad at me T.T). Also I want my program size to be small. Then again, I really wish this program had some built in song so I can use it as an web demo, and it would be a lot more convenient for testing. Maybe I'll ask around.
Hurt notes
Probably not possible. How hurt notes are implemented in lot these mods is by giving notes a 'name'. Like BadNote, or HurtNote. Problem is that I don't believe modders use the same name for these. So even if I could make hurt note work on some, it may not work on others.
Background
Same with custom skin.
Midscroll
Maybe!
Accuracy and ratings
I'm not sure what accuracy and rating system I should implement. I could always pick one but which one do I pick? Also, it feels kinda weird giving a rating when a player can jump to arbitrary point. So probably not.
Again, thanks for the detailed feedback!