Is there such a thing as a non-user facing system with a user interface?
Server hardware is generally not user facing (well, everything is "user" facing considering who the "user" is, maybe better to say "end-user facing") and has interfaces, both hardware and software usually, on one or another level.
None of those interfaces are user-interfaces, though.
Yes, anything that sits between a human and the inner-workings of a computer is a user-interface. That power-button on the panel of the server hardware? That's a user-interface.
Presumably you'd just use ordinary Python there.
Ok, we've put that in the title above.
(Submitted title was 'BeeWare – write Python, run as native everywhere')
And not even that. Unless they are pretending that GTK+ or Qt or whatever they've chosen looks native on desktops.