I am quietly going to say, again, that a way to temporarily suspend your pledge (perhaps with something like a 12hr cooldown period before and after to avoid any kind of immediately obvious exploit) would kinda solve the problem?
So long as it destroys any PP-specific commodities or data you're carrying when you suspend it (and you also lose access to all your rank benefits), I can't see any exploits that don't
also already exist for dropping and repledging entirely [1,2], which they've said has no penalty or cooldown beyond loss of rank, and the rank loss only affects you rather than the system progress as far as I can tell.
Maybe it needs a slightly longer cooldown than that because you don't lose the rank; equally, if Frontier are expecting it not to already be exploited because people are worried about losing the rank they're going to need to correct that pretty quickly anyway.
[1] This is possibly one of the reasons things like bounty hunting grant progress when you get the bounty, not when you hand it in, thinking about it.
[2] The most annoying of which I can think of now is a PvP one tricking people into getting non-Power bounties/notoriety (and also no merits) by unpledging just before you explode, and that's fairly niche. A "takes effect on next instance change" is all the delay that needs, though.
I found out to my amazement that I was on friendly status with the Feds for some reason. So why not set it up so that commanders with a friendly status with a Power other than their own gets a limited pass to visit the other power's systems?
You were friendly with the Federation as a superpower, but not with either Zachary Hudson or Felicity Winters who were opposed (Federal-aligned) Powers.
(Superpower reputation is rather a "leftover" mechanic and they could probably scrap it entirely, I think, since it barely does anything)
But in PP1, there's a really clear line between "doing Powerplay stuff" (you're carrying PP cargo or have uncashed combat merits) and "everything else", so it's easy to set the NPCs to ignore "inactive" players. In PP2, just scanning the ships in front of you in supercruise on the way to the station is hostility.
I still don't see your case for random PP NPCs appearing at random locations on planets. AFAIK, they don't appear if you drop out of SC in space and still won't in PP2. So why should planets be different to space, especially when we are talking about, you know, spaceships, which normally spend most of their time in space.
I think the distinction is - and should be - "do
other random NPCs appear at this location".
If they do, then you can do Powerplay things to those NPCs (scan them, shoot them, scoop the escape pods, etc, not all of which will generate a hostile response from those NPCs directly), and so Power NPCs need to show up from time to time as well.
If they don't, then you're not going to be scoring merits there, so there's no need for Power NPCs to show up to stop you.