You are (like so many other people) confusing IPP the protocol with IPP the driver, which is honestly not your fault and a terrible naming mistake.
And like you mentioned, people have way older printers because if all you do is print monochrome and mostly text, a printer from 2004 doesn’t lack much aside from AirPrint / Mopria. Which is why I suspect CUPS will not deprecate at least PPD drivers.
So yes, CUPS itself will only support IPP without any printer-specific driver. Since mobile phones also only directly support IPP this sounds like a reasonable decision.
Ah, yes. Thanks for pointing that out! I wonder how much more secure that will make things for those who have to use legacy printers.
> Since mobile phones also only directly support IPP
Technically AirPrint is not IPP Everywhere, they use a different raster format and some different glue. For example my Brother printer supports AirPrint but fails ~50% of the IPP Everywhere self-certification tests. But that’s splitting hairs.
> As for printer drivers, those few printers that "need" them can migrate to standalone applications/services using the CUPS API to provide an IPP Everywhere-compatible Printer instance. PAPPL provides a convenient framework for easily creating these applications and porting existing CUPS raster drivers, and the following printer applications are already available or (in the case of Gutenprint) under development:
[...]
> ps-printer-app: PAPPL-based PostScript printer application that supports all CUPS/PostScript printers via PPDs and includes all of the Foomatic and HPLIP drivers.
So drivers will still be supported in a sense, just not directly by the CUPS daemon.