The binary package libsane-hpaio DOES NOT depend on the binary package hplip, not even indirectly, so the binary package hplip can get demoted to Universe.
the binary package printer-driver-hpcups also does not depend on the binary package hplip, but printer-driver-hpcups itself can already get demoted to Universe as we replace the printer drivers by Printer Application Snaps (this driver provided by the HPLIP Printer Application, hplip-printer-app).
So hp-scan as part of the binary package hplip will go to Universe, hp-sendfax as part of the binary package hplip-gui is already in Universe.
The binary package libsane-hpaio DOES NOT depend on the binary package hplip, not even indirectly, so the binary package hplip can get demoted to Universe.
the binary package printer- driver- hpcups also does not depend on the binary package hplip, but printer- driver- hpcups itself can already get demoted to Universe as we replace the printer drivers by Printer Application Snaps (this driver provided by the HPLIP Printer Application, hplip-printer-app).
So hp-scan as part of the binary package hplip will go to Universe, hp-sendfax as part of the binary package hplip-gui is already in Universe.