"Moreover, if mankind ever expands into space, it would be rather naive to think that earth's nations would play a role there in the long run."

Assuming some sort of breakthrough in cheap propulsion and living systems, I couldn't disagree more. If anything, you'd see efforts at a sub-state level with the early colonies in the Americas given as examples.

I think that states, and particularly nations, are well suited to large scale efforts with minimal or no immediate payoffs. It's hard to get a sufficiently large group to pull on a rope at the same time.