The wording in the AIP regarding RNP 4 is a little vague. The only mention of it is in the
ENR section where it talks about ADS-B services in the Edmonton FIR (section 1.6.3.1). It says RNP 4 is required where VHF voice communication is not possible, but the map they show indicates you'll get VHF voice in all but the most extreme north (Axel Heiberg Island, Ellesmere Island, those types of spots). I don't see anywhere where RNAV 10 is discussed.
With that all being said, there are some spots over the NWT and Nunavut where I've seen the FMC transition to RNP 4 on its own, and to be honest, even though we're well within 60 minutes of an airport, they're sometimes not an airport I want to go back to unless I'm on fire. I'll still run the track and distance checks and plotting on Jepp anytime I'm north of 60 and not going to Yellowknife or Whitehorse and back, but thats just for practice. I've noticed most guys and gals I fly with do them too, even though it's only required by our ops manual for oceanic airspace.
If someone knows different though, I'd love to hear about it, because it's a common question at work too - whether we're working too hard or not.