In PVP Areas it is called Guild-PVP. So it have nothing to do with Factional PVP. Plundering in that case would only work if and really if you turn on the factional PVP.
Permitted still by game mechanics, I imagine ... I don't know that anyone has tried ... but that's never been "descriptive" from an actual game play standpoint.
Was also a time when it was basically a pick up game at SN's. Teams were mixed guilds, mixed factions ... players came and attacked some folks not others regardless of faction. Was a time when only 2 people would be at SNs. When busy ... somebody would run up to a digger axe in hand, see who it was and turn away ... others would avoid anyone with a weapon and only attack those who would not engage.
I support any and all chnages / additions to pvP folks as long as it does not take anything away from those that choose not to participate