We all know that empires don't become rich at the same pace so here is a suggestion.
Lets get rid of pirate timer and make them random in intervals from (let's say 10-15 min) so we don't really know when they are going to attack and let make them attack all empires in the game. Each empire would be attacked by force depending on how rich that empire is + bounty on that empire. They attack planets with most trade ports and least defense. If there is no trade ports they try to go steal technology.
They have constructors and factories on pirate base planet.
Ships are able to jump directly to the planet they want to attack (no phase lanes for pirates and while phase jumping their ships are visible to all empires + reduce speed with which they travel trough phase space). This way don't get stuck in others empires gravity wells and empires have time to go defend). They attack with ships that have ability similar to sovas' embargo (perhaps 50% of planet income + trade ship stays in gravity well).
They have no pillagers but have ships with kill population on planet, capture module and capture constructor abilities. If they capture constructor they can build defense platforms and factories which can build additional ships -- depending on how much money and minerals they have.
Their ships stay in gravity well until there is a overwhelming force present to drive them of. (They retreat to pirate base similar as AI does if attacking with much stronger force).
They don't capture or destroy trade modules since stealing is their important income.
When they capture Labs (they can capture only military) they do research (no tier handicap - more labs just mean faster research) which stays with them even after those labs are lost and they can infiltrate labs and steal all research that empire did together with ship designs.
Armor, hull and other Weapon research stacks so they can get Tec missile damage increase with Vasari phase missile. Same would go for hull, shields ect. (if they steal 2nd vas hull research, 1st Tec hull research and lets say 3 rd Advent hull they get hull increase that combines all this research).
This way empires are forced to build defense on all planets.
While pirates are attacking their ships are away from pirate base which is lightly defended (defense platforms + limited ship force). Until they steal enough and build more ships at pirate base it is weak and fairly easy to kill (it does have enforce loyalty so u cannot kill them completely). If there is no force present there pirates will rebuild and once their base is sufficiently defended and they build enough ships they will start raiding again.
This way even when empires are at war they have to work together to get rid of common enemy since if they steal a lot of technologies they get really strong with massive ship hulls and armors. In diplomacy option there is mission to attack pirate base which all empires are eager to fulfill as long as they see that other empires are attacking as well. While in pirate base gravity well with mission offered there is a cease fire (sort of akan lvl6 ability) between attacking empires but just until mission is offered and just in pirate base gravity well ...... every where else war as usual.
PS let me know what u guys think