I think the panels are currently not affected by activities, i.e. they remain the same across activity switches.

Applets on the desktop, wallpaper, etc seem to be per-activity

Getting rid of what? Wallpapers? The ability to have different ones per activity?

You can have different wallpapers (and different widgets and all kinds of other things) per activity.

I think the focus of the article is on that specific device as this is the one the developer had access to and personal need to get it to work.

The chosen approach of adding support to an existing kernel driver and libinput suggests that any changes above, e.g. in Plasma, should work generically across similar devices as long or as soon they are supported on the kernel level.

That might already be true for the device you have or could have been enabled by these recent changes.

In the worst case it should enable someone to make similar additions to the low level stack without having to worry about the levels above. E.g. by a driver developer who doesn't necessarily have development experience or setup for desktop changes

Not just window position. Also size, which screen, which virtual desktop, which activity, state (maximized, etc)

Probably just replacing "KF5" with "KF6" in the cmake file and changing the version from "5.90" to something like "6.0" (or higher)