System revolts are currently a bit lackluster in that all it does is create a Pirate fleet with some of your hulls. Vodyani pacific conversion(SLC) tech equivalent is just garbage, you pay the price of a full-on system conversion for one dead pop and 500 Essence. I offer a solution to both of these problems in one. 


Create a mechanic where a system in revolt splits off of its parent civ and becomes sort-of like a Minor Civilization, except no Assimilation Trait(for balance reasons) and uses the ship hulls of its parent civ instead of Pirate hulls. It'd start out at War with its parent civ, and could be reabsorbed either through military means or by calling for Cease Fire and then using the same diplomacy options that exist for Minor Civs.


However, those same diplomacy/war options would exist for other empires as well, making it a priority to get the system back if it had any good improvements, lest another civ decide to Assimilate the rebels for themselves.


Finally, Vodyani Pacific conversion would cause a similar split-off from the other empire to happen instantly in the system converted, however the new "rebel" system would start out already Brainwashed by the Vodyani, making war the only option to take it back and also providing the Vodyani with tributes for as long as it stays like it is.


As for the unique actions that Minor Civs have(Dev Grants etc.), you could do it any way you liked, these rebel systems will really only exist if someone is struggling anyway so it wouldn't be too unbalanced to just select a random action from the three to assign to each rebel system as they're created. But it's up to you, you could even leave these actions off of the rebel systems altogether.


Be sure to like this if you wanna see it in!