I don't want a first person shooter. I was very disappointed when Elite Dangerous started going in that direction. I bought the game to fly sweet space ships, possibly in formation with friends. I just want to do cool space stuff.

I think there's a case to be made for galaxy-wide sandbox gameplay. The truth is that space is empty and it's up to us humans to make it not so. The Subnautica-like basebuilding found No Man's Sky is a major source of fun in that game. It's what makes the galaxy feel alive and dynamic. Elite Dangerous lets you land on planets but there's nothing to do but admire the scenery and take screenshots when you do.

Kerbal Space Program is a single player game which also has mostly empty worlds but it's also a sandbox game. I can build and launch a space station piece by piece. I can later use that space station as an orbital refueling station to reach more difficult planets. I can land on nearby planets and set up a mining operation to refuel the station for the benefit of future space missions. It goes on and on... KSP2 was disappointing not because it didn't have FPS or diplomacy gameplay but because it launched without these features of the original as well as massive peformance regressions.

Corollary: The type of designer who likes to build space simulations also has little ability to self-regulate feature inclusion.

Solution: Never let such a designer run a project themselves, and instead pair them with a practical and empowered project manager.

The ultimate game genre has the ultimate allure.

No Man's Sky managed to pull most of that off. The diplomacy stuff is a little lacking, but it's there.