If it has more than 7 minor factions in
If has no starport
If it's lore important
If it's permit locked
Afaik, a fleet carrier can mess things up, but that's not been seen by me on official lists of things
If more than 500ly from Sol
If has any player minor faction or NPC minor faction that's been adopted by a player group
When applying, you must at one point choose Fed, Emp, All, Indy, then you choose government type, like Democracy, Dictator, Theocracy, Corporate. Then your up to 3 choices must match that. If you choose Empire Patronage, your 3 choices must be already controlled by Empire Patronage minor faction
It can't have a rare commodity either, like Fujin Tea, Xihe Alien Pets etc
I'd say get a list of 6 to 8 and rank them too.
We copied and pasted the relevant 2000 systems into excel, then looked up each one and deleted the row that had PMF in. That left 84 for our category of system. Then we went through the list on Inara, went by number of stations, how many PMF in neighbouring systems there were, distance from the star etc