quatermass: There is a lot of Linux stuff out there that could be ported and a lot of it duplicates functionality found in other software. I cannot see a reason why we should need to port HP's drivers as well if gimp-print gives good results with the printers in question.
In addition, HP's drivers are add-ons to ghostscript, so we are back to printing through PostScript with all its limitations. Yes, a printer driver based on GhostScript is conceivable as well but I have chosen a different approach. Nobody stops your or anybody else from creating a ghostscript-based driver.