Let's hope that commonsense prevails, then, when the documentation catches up
Traffic at F360 is within MNPS airspace and is therefore MNPS certified; having all the benefits of reduced lateral/longitudinal separation. Non-MNPS traffic above F420 does not have the required Nav capability/accuracy/redundancy to enjoy the reduced MNPS separation and must therefore be treated differently from those who are MNPS certified.
.- I'm afraid I do not understand the logic here. I would suggest that very little traffic operating above the MPNS levels is not 'certified' - I suspect it almost certainly is but simply wants to fly higher, but indeed going for the mid-point is sensible to 'cover all'. However, going back to the OP, on which track does one base your (existing) 15nm offset for descent? I would choose the same 'mid-point'.