@Golden_Syrup Do remember that most expeditions and arks quest areas are semi public and allow 12 people regardless of their party status. As far as I understand, these areas are not hosted by any player but by the server itself (will need a confirmation or a correction to this part, though). Unleashing pvp in those areas, in my opinion, wouldn't be healthy for a certain group of players, and that includes me. And considering the various kinds of players with their varying powers and skills, I don't think it would be too fair to trigger a pvp event in such a place. I mean, we know what kinds of players love to be unleashed onto unsuspecting newbie and weaker players. And it has never been a good sight.
Which is why I'd stick to the pvp enabled and pvp disabled area idea. PSO2 can do this through assigning blocks people can willingly go to. That way you weed out anyone simply wanting to stick to pve. More on a game that has been historically a story pve focused franchise.