Linky

Why wouldn't it run on Linux? I personally think it will for 2 reasons: 1. The original game runs on Linux. KSP-2 is built using the same engine (Unity), and I can't see why they would drop support. 2. Cheating slightly, but Proton compatibility is getting very good. Multiplayer is up in the air (Proton often does not agree with DRM), but the single-player is confirmed to be DRM free. I hope it supports Linux. I daily drive Pop!_OS, and only use Windows when I need to, such as playing Star Wars: Squadrons.

Is it Sarnus?

Personally guessing there will be at least 10 star systems at launch, could see upwards of 15. We probably haven't even seen 20% of the planets that weren't in the original, and we know of 8-ish new planets and moons (that is without going back over everything they have released, though). My hope is that they will add a new star system each year.

"Due to the continued research by KSP's dedicated quantum physics department, we are excited to announce that we have discovered parallel universes! These alternate realities are more or less the same as ours. A recent breakthrough allows us to be transported through the 5th dimension to 'sync' up with these alternate dimensions to team up with the Kerbals that live nearly on top of us!" This won't end up happening in the game (although it seems none of us quite have an idea that would fill every dependency), but my thought process is that each player has its own universe, with a new device that allows you to sync up with other realities when necessary to work together. You do your part, then click "SYNC", where your progress appears everywhere. Perhaps a "main" reality? Still, there are a tremendous number of holes in this idea.

I don't know if anyone has said this, but the ability to build the payload and rocket separately. I typically use variations of 2 - 3 rockets of different size / range to launch everything, just switching out the payload. (I do occasionally switch out the upper / kick stages for longer range. I tend to build smaller things, so NERVE is great for sending 10 tonnes to Duna.) I know a lot of us want life outside Kerbin. People seem to like friendly sentient aliens, but I really want a pet of some sort. (a dog that follows you around and sniffs out stuff would be an interesting mechanic.) Life of any sort on about 1 planet from every 10 systems would be great, if it was varied enough. A black hole system might be interesting too. Not sure how you'd simulate that, but please give it a shot, Intercept! You can add content to the game with updates! We don't mind!