Some firearms would be cool, and it would be great if they have some architect technology. I think besides weapons it would be cool if they were a part of the story/needed to succeed in it. For example like Leviathan brain juice is a crafting resource.

I want a underwater tank in subnautica

Also i want a base attached laser smth like this:

It's not gonna happen, the developers have stated they don't want a lot of weapons in subnautica games