My thing about it is designing for both an isolated feel and a cohesive co-op may be impractical, and I'd prefer they focus on the part of it that makes it really stand out. There are also things like how do you progress world events, can either player trigger them, do they have to be in the same area together, etc which all adds design overhead.

I also want more good co-op games they're a lot of fun. Personally I don't think this is the right series to target for it though, but also idk what direction they're taking it so co-op may fit well with the new one.

I just want more co-ops in general. They, and the racing genre, are two things that are dying that I'm sad to see go.

There is a mod that enables co-op for Subnautica. It was a pretty fun, but when I played it a few years ago, it didn't really add anything, it was just that you could have two people going through the story together and harvesting resources etc.