I'm confused, where did this whole thing of PP = PvP thing come from? As far as I am aware, other than Sandro's one statement about considering open-only and a single sentence in the newsletter about how it gives a reason for PvP against other factions, FD have never stated that Powerplay exists for the purpose of PvP. The whole original sales pitch for powerplay, both in the newsletter as well as on the old ED official side (now retired), was that powerplay was all about signing up to one of the powers to oppose the other powers.
That's it: power vs power. When I sign up to Hudson, I sign up to serve Hudson, fly alongside his fleets, deliver his goods and run his missions and oppose his enemies. Not signing up to some inter-player conflict as part of some Pilot's Federation civil war. It's between me and my power, with occasional conflict with other powers, not between me and a load of loosely affiliated gankers out for blood.
Trying to shoehorn PvP into powerplay is basically saying the real match after a game of football is the post-match fight in the pub rather than the one on the field. It's about the players and their supporters, not about the informal brawl between the supporters; similarly, powerplay is about the conflict between the powers and how we support them, not about the Dominos and Papa John's pizza delivery guys squabbling in the parking lot.
And, just for good measure, I'll sum up my points on the previous topic regarding this: Powerplay isn't played much, not because it's not open only, but because it's rubbish.
Making it open only simply means that you are left with a piece of open-only rubbish where the content is from other players. This is in addition to consigning it to the limited PvP crowd and excluding those who want PvE as well as reducing the incentive for FD to ever actually improve it into a cohesive and interesting set of mechanics.