Unfortunately, doing Powerplay (a consentual, competitive player vs player activity) in Solo/PG does infringe on Open powerplayers. In Open play, there's risk of running into hostile players which forces you to compromise on your ship-build and strategies. In Solo play, there's no risk of losing a load of forts or expansion cargo. NPCs cannot provide a challenge for players, only other players can.
There's no viable, meaningful playstyle for organic pvp players in the game and that bores many pvp'ers. Which I believe leads to ganking and griefing. A sort of vicious cycle, if you will. Powerplay is in an awkward spot, with no real gameplay reason to exist in its current state. BGS hauling, exploration and combat are more varied, more profitable and more refined.
I don't see why not take an activity which pits playergroups against each other, and making Powerplay the outlet for consentual organic pvp in Elite. Open-only is one change I think is required, which removes the allure of the safety of PG and incentivizes players improve their skills, ships and teamplay in order to be more effective.