Similar to the Touchpad KCM we want a separate Mouse KCM on Wayland speaking to KWin via DBus. Currently there is only a workaround in KWin to read out the X mouse speed value.
The plan is to basically to mostly copy the Touchpad KCM code. Most options should be the same anyways as touchpads and mice both are pointer devices.
Relevant bug: https://bugs.kde.org/show_bug.cgi?id=350688
Relavent prior patch: D8798: Add xf86-input-libinput support for X11 mouse backend.
It would be nice if, as a part of this, we could also improve the usability of the Wayland Mouse KCM the same way we (you?) did for the Touchpad KCM. The most common task--changing the cursor speed--is rather non-obvious in the current X11 implementation.
If we work on this new KCM, can we use this image as a guide? This is a system settings design proposal that Marco is also intending to work on. Maybe we can use it for this Wayland KCM as a guide.
Sorry, but the Wayland KCM will use Libinput, what means a KCM with way less complexity in comparison to the old one. It will look more like the current Touchpad KCM on Wayland. I.e. just a few buttons and one slider. I could try to use @mart's new form layout though.
This means also that @ngraham's wish for better usability should be fulfilled.
Potentially relevant/mine-able for inspiration: D8168: kcm_input: Refactor the code and add support for libinput under X11
Let's make sure we expose middle click emulation (i.e. middle click when both the left and right buttons are clicked at the same time). This was recently requested in https://bugs.kde.org/show_bug.cgi?id=383379