Note, that this would not be my personal preference, I'm happy with teh modes we have now, just throwing it out there as a compromise I could live with, as a BGSer and semi serious pvper...
So, if your pvp flag is down, you cannot be interdicted by players, and your ship cannot be damaged by player weapons, munitions or rams from other player ships.
When your pvp flag is up, the game is exactly as it is today.
Your PvP flag is raised automatically when (this is just an initial list, we can expand on this and refine it

):
Being in a hostile control system while pledged (we can expand this to include systems being expanded into, prep systems, whatever, I don't pp much you guys can discuss the specific circumstances)
Being wanted for player murder anywhere
Being in a populated Anarchy system
Entering a Combat Zone
Entering a Compromised Nav Beacon
Entering a HAZRES
Transporting anything from an approved list of 'piratable materials', which includes most of the high value stuff, OR transporting a total goods over a certain value.
That last one's contentious, but you can't kill pirating...maybe keep the list specific, anything of equal or higher value than platinum, for example. Like I say, this is rough, we can refine.
It needs to be fair to PvEers, but also to PvPers, compromises and all that.
Any support?