It will still be a problem. The ØJenquai will be able to pick the other empires apart system by system. - Jump from a safe location (empty system) send in a fleet with closers and close the system off. If this don't succed, another 20 turns of boredom until the next fleet are ready, then try again.
To make the mod playable you could also make openers/closers available to the other races but at an insane price (something like 10 times normal researchpoints). That would give the Jenquai a limited time to take the other guys out. Not sure if I would want to play such a mod anyway though
