Don't get me wrong
You have mixed concepts quite a lot.
An X terminal has absolute no relation with XDM PROTOCOL.
The XDM PROTOCOL (and all applets which implement that)
is a NETWORKED DISPLAY SERVER aimed to control multi user
access with proper authentication and proper management
of hardware requirements.
It is fully aware of authentication and capable of handling
several users and several displays on a single instance.
Quite the opposite of what systemd and wayland are doing
or trying to disrupt all those tools to put the single display
and license fee model on top of the stack
Forget about any "Terminal" - replace this word with
"DISPLAY MANAGEMENT SERVER"
then include OpenGL aware virtual hosts as well
https://virtualgl.org/to leverage your vision of things being disrupted
and mocked by system vendors
A whole above level of system services than
that deep shit pushed by MS and systemd goonies
Just google now for DISPLAY SERVERS and Virtual OGL
Paul