From what I can tell, Open only for PP2 means if you are pledged, you have to remain in open. It doesn't seem like there is any way for the game to separate working for factions from powers with PP2.
I don't think that's what anyone's asked for at all. All the calls have been for specifically powerplay transactions to be counted in open mode - so if you're between missions and don't
have any powerplay business going on, you're free to log into solo/private and do whatever.
As for how possible that is, that really depends on exactly how pp2.0 even
works. Like, opposed conflict zones are a bit of a no-brainer, they could be made to only spawn in open. Something more nebulous like "delivering exploration data" less so.
And then you get into the nitty-gritty of
defensive versus
offensive actions. Notably hauling fortifications, the noncombat action in PPv1, is purely defensive. You can't
attack anyone by doing it, only shore up your faction's defences. Undermining, on the other hand, is a combat action, an
offensive combat action, wherein you deliberately go into enemy territory in order to attack that enemy.
One of the biggest arguments that keeps coming up is that people don't
like being attacked by an enemy they never see. It's like... the same way people get mad at offline raiding in rust. Of course this could be entirely moot depending on exactly what 2.0's activities entail.