My position still stands in favor of being able to hire pirates and rebels from other factions.

Give Pirates a TEC starbase with sov protection vs bombardment and hangars, but little else so it isn't overpowered.

Instead of Truce Among Rogues, create "Outreach" like we did in 7DS.  It's a tactical structure using tradeport mesh, but through it (for Rebellion) you could hire Pirate, Advent, and Vasari which would spawn (like return armada) at your planet for a certain amount of credits, metal and crystal (tribute) and fleet supply.  Hiring pirates or paying tribute to gain the assistance of other rebels out there would be more in keeping with the TEC, but could also be something useful to the Advent and Vasari rebels and it wouldn't affect the players ability to stomp hell out of the regional pirates and militias for XP like everyone else.

With some small changes to entity files, there could be a "Merc" version of every faction that has 10% better weapon damage since you can't research enemy weapon sytems.  Ship with abilities that require research would be an issue since you can't research enemy tech to unlock them, but spawning light, heavy, and carriers should be enough.