I don't like the idea of having to look for and find all the needed pylons to close down the primary rift and then just have that happen no matter what. I'd rather have the pylons be a found ruin installation or ground force component that after finding you can research and replicate yourself, if not easily. A pylon would also be a structure that would need (X) amount of people to work or a Static unit not unlike STO weapons, but when it works it degrades any rifts in the system and prevents the formation of new ones. This would mean that it must be impossible for rifts to form in systems with no planetary bodies though.
The Ruinous Powers rift beings can send forces to destroy the pylon though, it just lets you avoid having to station a full blown warfleet in every system in your borders just in case a rift forms there. Rifts could still contaminate bodies in a system though and invest ground defenses in them, so that getting that pylon in place and operational for long enough to close a rift and prevent the enemy from destroying it is something that requires actual effort. To prevent the game from slowing down as it has to handle every body in the rift zone with their own planetary defense force stationed there, it'd probably be best to have them spawn when the rift achieves a certain strength and non-rift being forces are on planet, and despawn if they're the only thing left.
Closing down the primary rift would require more time and forces as the rift beings defend it more thoroughly, and I'd say that the rift beings can also cheat the normal pathing system. They can use the rifts to jump from a secondary rift to the primary rift, and from the primary rift to any secondary rift. Given how much Aurora depends on the jump point mechanics, that's some pretty potent boost.
