… aaaaand of course as soon as I post that, I find a reasonable workaround, for printing at least.
It seems that a driver does come with CUPS for the printer (“HP LaserJet Pro M148f-M149f”), and I can select that printer driver manually via the printer properties “Make and Model” dialogs.
A headscratching caveat: Print Test Page from printer properties doesn’t. No idea why not. But printing from apps works fine.
This of course doesn’t help me with scanning (it’s one of those AIO printers), so it would still be useful if I could find a way to upgrade hplip to get that working.