-Astral gate should be an industry, not structure. IMO.
Typically industries in Starsector produce a commodity. Even the military base produces crew. That is inconsistent with making the astral gate an industry,as it does not produce a commodity.
-Astral gate should consume large amount of some kind of resources. Heavy machinery, fuel, crew, volatiles, transplutonics... pick any.
I'm currently working on a new industry that can only be built on planets with ruins on them. It will produce "Domain-Era Artifacts" corresponding with the size of the ruins on the planet. Ultimately I'm going to have the astral gate, Kletka simulator, and all my terraforming structures demand that commodity (optionally of course in case the player doesn't want to use that industry/commodity). The astral gate will demand an enormous amount of them, forcing the player to find a vast ruins planet to colonize before they can profitably run an astral gate network.
-It is weird, you can build any structure/industry on gatekeeper station. Isn't it should be specialized? Orbital works (NF) + fuel production (ST) + light industry + all demands supplied in faction, makes station profitable even without AI cores. Using AI cores makes it a money river, not a sinkhole it should be. Suggestion to forbid building all the industries except commerce and military base. Alternative, that industries can have some kind of penalty to production/income not to be over-profitable.
Unfortunately it's not possible for me forbid construction of vanilla structures like I can with my own modded ones. I agree that there is a balance issue with the high revenue that can be generated by the gatekeeper station, but in my upcoming patch I hope this will be counterbalanced by the need to complete a quest to unlock the astral gates and the need to have a vast ruins colony with 100%+ accessibility. This should prevent the player from generating huge revenues from the gatekeeper station until they reach the late game, in which case they will have almost unlimited money anyway.
In addition, I think many players use the "Cramped Quarters" option to effectively limit the size of station markets. The astral gate has the same upkeep regardless of market size, while profit-generating vanilla industries will be less able to counteract the astral gate upkeep if they aren't producing much due to cramped quarters keeping the gatekeeper station market population low.
Something I'm going to look at is increasing astral gate upkeep based on the amount of exports and/or market share the gatekeeper station has. That way the huge income will be "taxed" down to a more reasonable level. I do want to maintain some level of profitability for the gatekeeper station market, as access to a pseudo-gate network would be extremely valuable economically and people would rush to start businesses/industries nearby to gates.
-Gatekeeper station should have a colony condition that decrease stability and population growth. It is dangerous place to live.
This is resolved by enabling the cramped quarters option in the settings. I hope that vanilla/Nex get a similar feature, because the only reason cramped quarters isn't the default setting is because I want to maintain consistency with vanilla/Nex station behavior.
Bug: you can abandon gatekeeper station, but gate still active and you can use it for free. No monthly upkeep.
Thanks for bringing this to my attention. I'll correct this in the next patch.