Comment # 22 on bug 1120405 from Takashi Iwai

Actually you don't have to support the serial device in X driver at all.  The
only requirement is the inputattach program that triggers the kernel serio
binding and the relevant systemd unit file.  Then everything else is done by
kernel side, and even Wayland would work as-is.

For Leap 15.0, IMO, we should put back the inputattach and the unit file. 
(Note that the udev rules still contains the trigger of this systemd unit
although you removed the actual files.)

For TW, it's another question.  Basically you don't have to install wacom X
driver to enable this serial device at all but only inputattach and systemd
file.  So I guess we can consider creating a sub-package.  (Or even drop the
old inputattach from gpm and share with the new one.)