I've kind of said all this before, and it is essentially an anti-FAF post. But I am curious about what motivates talented people like @Jip to add features to mainline FAF rather than creating a fork, mod, or their own game.
In my opinion, if you are a good programmer and smart game designer (or think that you are) you should work on your own game instead of contributing features to this community of people who don't want your features. It sounds like a very mean thing to say, but I really don't know why people want to contribute to FAF. I have decent programming skills, have watched/read a massive quantity of game design things on the internet, know a lot about FAF, and am even one of the highest-rated players on FAF. Outside of some very brief moments of delusion, I never considered contributing to FAF to be a reasonable thing to do.
Even if all your ideas are truly amazing and make the game way better, it will still be a dead 20-year-old game. You will get no merit or money or anything for your effort. Everyone will be mean to you on the forum no matter what, and you end up in miserable forum threads like this one. The only benefit I see with contributing to FAF is that you have a pre-existing captive audience, so it is to some degree impossible to fail and you can feel like a smart and successful person and get fans and whatever. The downside is that this preexisting audience is old people playing an old game, so you can't treat it like your own early-access indie title. If you do the bare minimum to keep the project alive it will probably go fine, but even if executed perfectly, getting feedback and implementing new things will have large amounts of friction.
There are finally some reasonable competitors coming along to fill FAF's niche place in the market. Either work on one of them or start your own. Or make something totally different. You will probably still be subjected to the same toxicity as here, but at least you will have your own thing, make money from it, and leave your mark on the world. When I'm not too lazy and depressed to work on stuff, I work on my own little game project. If I ever release a game, I fully expect to encounter toxic assholes like myself, but since it's my own game I can just do whatever I want and tell them to fuck off.
In my twisted view of the world, the toxicity of FAF is somewhat beneficial because driving talented people away to make new things is better than having them contribute to this dead-end project. I thought the people working on [redacted] were pretty cringe and annoying, but since they went off to try their own thing I have a lot of respect for them and look forward to seeing what they accomplish.