I have been trying to argue for PP to be done in open only, since with the current design its a dead horse anyway, so what worse that could already happen, make PP an exclusive PVP content.
Sure, but you can't have the Rank 3 module rewards then.
People who don't want to engage murderhobos shouldn't be truly forced into Open to get these modules.
Personally, I'd argue that it would have made more sense for PvE players to be enticed into PP by putting the actual current Merit mechanic into Open (so all system ownership changes are done in the Open mode), and then giving PvE players some kind of merit system of their own, where they provide CC at a
hugely weighted ratio (1 CC from 10,000 merits, for example) for trading with/doing missions for the local power that the current PP faction wants to support, or they provide a
very slow/small increase to fortification of their system by bounty hunting in that system.
Something more inclusive that would serve as a hook to get people into PP.
Then you can try and convince them later to move into Open for the other stuff, as they get more interested (is that even possible?) in the other parts of it.