I could see a potential problem with the System Gravitational Shield Facility, if the game is long enough to allow the players to have access to that facility. (Level ten in Shields, not that easy.

)
The problem with this facility is that it prevents any warp opener to this system (among other abilities), so the system would be virtually unassailable. And I would say you could still open warp points from this system to others, I am not sure though. If it is the case, then you could be impossible to attack and still able to launch offensives. (If you remember to close one of the warp points you used, just in case)
Apart from that, this mode would be very fun, shame that there is no warp opener in the events.txt. But maybe it could be done? I will have to check it out.