The elephant in the room is that IP are not allowed to have a leader...
nor have any kind of government choice...
A Pirate IP without a leader would be dull...
Maybe besides IP there could be a new class of "IP" denominated "Revolting Powers" which could have a leader assigned, and
work as normal civs but with some limitations (no settlers expansion) and could form a "League" like the "Hellenistic" league that
then became Greece once large enough... (or better say, after nationalism has been "discovered"... Greek cities where called Magna Grecia but it was more of a geographical term, the concept of nation did not exist..)
It's a interesting concept, very complex also.
"Revolting Leaders" for "Revolting Powers", or possibly a Revolting Leader who causes a City State or a Settlement to revolt would be interesting, except that we already have some of the most iconic Revolting/Revolutionary Leaders in the game:
Napoleon of the Consulate
Lafayette
Rizal
Trung
Obviously, there are a host of others from the historical record that could also be included, but it emphasizes the problem: what's the real difference between a Revolutionary Leader and a regular Leader? How they appear? Who can get them?
I guarantee if, say, Leon Trotskii was included as a potential Revolutionary Leader there would be an immediate cry for him to also be a regular Leader - and almost any other 'Revolt/Revolutionary' Leader you can name: Lenin, Robespierre, G. Washington, Ollie Cromwell, the Roman Grachiis, Alcibiades of Athens - any good or iconic leader will be desired for a regular Leader, too.
Also, while Leaders for recognition purposes are almost a requirement for playable Civs, for an in-game event that produces (presumably) an itinerant effect like a CS or settlement revolt they are not so necessary. Have a specific Revolting Masses unit graphic (or a singular Pirate Ship unit for a pirate CS) and for the few turns a 'revolt' lasts, that should be enough. Especially since, presumably, we would ultimately desire the possibility of the Revolt producing a new independent City State or even a playable Civ - in which case regular unit graphics and Leaders should then apply.