This may not be what you had in mind, but the bzr branch I just associated with this bug adds a new per-seat 'xserver-vt' option. If 'xserver-vt=0', then:
* VT switching will not be performed for the Seat
* the "vtXX" argument will not be passed to X
* the "-sharevts" argument will be passed to X
* XDG_VTNR will be left unset
This may not be what you had in mind, but the bzr branch I just associated with this bug adds a new per-seat 'xserver-vt' option. If 'xserver-vt=0', then:
* VT switching will not be performed for the Seat
* the "vtXX" argument will not be passed to X
* the "-sharevts" argument will be passed to X
* XDG_VTNR will be left unset