I know this seems pretty pedantic and obscure but airports with exclusively P-RNAV departures are becoming more and more common (as IO540 has noted in other threads) and I am interested in whether the rules are routinely being ignored or are instead just misunderstood.
IME, the whole thing is just ignored.
ATC couldn't care less how you navigate providing you are in the right place. The PRNAV stuff is seemingly only at airports big enough to have radar (or a radar feed).
And if it was taken seriously, the great majority of traffic could not use that airport.
This begs the question of who actually decides "hey we need to make this place PRNAV" and why. Some manager who has just come back from a Eurocontrol seminar, perhaps? I've been to some of those and the officials (well, usually one very arrogant individual) make a very forceful case, which sounds good if you are not a pilot yourself, and most airport managers are not pilots.
IMHO, what would be a real problem would be if
enroute airspace became PRNAV-only. Then, Eurocontrol could enforce it at the IFPS flight plan validation stage - like they already enforce 8.33 (if filing above FL195) and RVSM. There is a database, I believe, of PRNAV approved aircraft, and this can be made accessible to IFPS, or even to ATCOs. I have been told by UK ATC that there is a proposal in the pipeline for making the LTMA PRNAV-only, but this stuff has been brewing for an awfully long time.