Island Sanctuary at Max Rank should give you something for Cosmic Exploration

[Jeeqbit]

You're not building a town in that content. There is no player driven progress in a constructed biome.

Unlocking the different sections is slightly. But you've edited your post to reflect it anyway.

There is no guarantee that Cosmic Exploration will be personal progress, because it could be like the Firmament since it is going to be more social. It remains to be seen whether the progress even is something you only see on your character or whether everyone sees it like how the Firmament became.

So far it seems like we will get seasons similar to the Firmament, except instead of building different sections we visit different planets. Unless they make us progress through these seasons like Bozja and Eureka areas so that we can still experience them further into the expansion.