from UNIX, I'd expect to be able to do
% setenv PRINTER ipp://spot.cs.utk.edu/slug
% lpr filename.pdf
(much like I do now)
and select a Print option which would pop up a dialog box that gave
me the option of entering an ipp: URL as an alternative to choosing one of
the preconfigured printers. (similar to the option that lets me type
in a network printer accessed by SMB)
In an really nice world, the printer chooser would then talk to the
printer and figure out what kind of driver it needed to print.
If the driver were not already installed, the dialog box would then
give me the option of either installing a driver from disk, downloading
one from the net (hopefully with adequate authenticity/integrity
protection), or using a generic driver to talk to the printer.
(assuming my system already has a driver for common PDLs)
Of course, the IPP group can't dictate OS vendors' user interfaces,
but I see no reason why the IPP protocol cannot be used in this way.