ping

This is going to be a necessity for Wayland, given that libinput is mandatory.

Wow, very nice! I'm still not sure if on Wayland we should combine Touchpad and Mouse KCMs to one "Pointers" KCM how it was proposed years ago, because their properties in libinput are very similar. But since you already did the work for adding multiple backend to the Mouse KCM let's go with two separate ones now!

Your change is very big though. Could we split it up in a patch series? Basically by your bullets point in the description. Then we would have the following patches in order:

1. UI in kcmmouse.ui.
2. Backend refactoring
3. Libinput mouse acceleration and revert scroll (on X)
4. Libinput macros
5. No revert scrolling for touchpads

Maybe (2) needs to switch position with (3) and/or (4) with (5).

Have you had any time to produce some more of the individual patches for this? It would be really great to get a libinput-compatible version of the input KCM for 5.12.