I can't really make any kind of coherent, detailed feedback right now, but I just wanted to express my sheer glee at the pirate alliances I tried out in a short game as TEC Rebels. Having the pirates both be on your side and send you reinforcements is not only incredibly fun and entertaining, but opens up a lot of new strategies with TEC mobility (ie. backdooring into enemy territory through the pirate base.) Additionally coordinating your attacks with incoming pirate raids, which admittedly you could already do, but not without the pirates taking potshots at you.
I might just play TEC again some more because of Rebellion.
One thing I was mildly concerned about but don't have time to test right now is that after I won (and promptly maxed out fleet cap upgrades and let it fill with pirates) I took a quick hop over to the other system and found the artefact planet.
Now I'm unsure if the enemies are supposed to be "friendly" and not attack you/be untargettable if the artefact planet wincon is off, but if they're not, then Honour Amongst Rogues may be causing TEC Rebels to be unable to attack them because they're technically neutral.