Wormholes

Not sure if it would work (it'd be a pain to test) but you could probably give them the research for it, make it free, take 1 second to research and see how it goes.

More than likely possible in Diplomacy see'ing as the Pirates have research by default but its worth a shot.

Probably more trouble than it's worth.  I think I'll wait for Diplomacy.  I'm probably going to upgrade my mod to Diplomacy anyway.  I was already having problems with the current Entrenchment diplomatic features.  Upgrading my mod seems less of a bother than trying to make the current system work.

You could try giving their base the artifact that allows wormhole travel on a particular map. Test it by only connecting the pirate base to a wormhole, and then have the other wormhole connect to the homeworlds. If you get a pirate raid to attack you, you'll know if it works.

Neither seems to work.  I piled the only pirate bases in one system connected by wormholes to the rest of the galaxy  Each pirate base had a wormhole tech artifact on it.  That works for the players, but there were no pirate raids until I actually entered the system.

I also ran in to the same problem, doesnt look like the Pirates are able to research either due to lack of Technology/Research structures are just down to the Pirate AI being completely unable to use wormhole tech

Even if the piratebase is setup like home planets in the Ancients Gifts map with the wormhole artifact and the planet fully explored they cannot travel through wormholes.  So the pirate AI is not able to use the wormhole tech.