xkb protocol (setxkbmap tool) also has no Wayland equivalent

[kkofler]

One item I miss in your list here, and also in https://gist.github.com/probonopd/9feb7c20257af5dd915e3a9f2d1f2277, is the lack of a standard protocol for setting the keyboard layout. See the discussion under https://github.com/calamares/calamares/pull/2180. The official recommendation is to just set the keyboard layout through systemd locale1, but that is not actually going to work without a reboot (if at all) in most situations. Under X11, setxkbmap works instantly for the entire session (and, at least in an installer context, should in general be done in addition to a change to the global system configuration, doing just one will not work as expected). Some Wayland compositors such as kwin_wayland have their own non-standard ways to apply keyboard settings to running sessions, but those are entirely implementation-dependent.