[Alneyan]

The main problem with Warp Openers would be the ease to reach the opponents, bypassing the lesser powers and heading straight for their world. The System Shields Facility will not work either, as it would still be possible to open the wormhole to the system next to your opponent. (Obviously, without the Ancient trait you will need to do some scouting to spot where they lie)

On the other hand, it would make going to the offensive much harder, and how could you do so if other lesser powers could attack you on the way? You might want to instead add a rule along the lines of "you cannot *attack* the lesser powers, but defence is perfectly fine as long as they are the ones on the offensive". (No, the best defence isn't a good offence in this case) I will confess I am not sure how it should work to put the emphasis on these lesser powers.