Depends where you think humanity-on-Earth sits relative to the Culture. Since most of the Culture is human and we on Earth are as yet unaware of any spacefaring civilizations, I view it as a possible future for humanity. I would not be surprised if we encounter other life in space, but I'd be extremely startled if it turned out to be human life.
Oh, you're right as an in-world thing. But I meant this sort of high technology described is in our future, ie I'm using 'in the future' as a proxy for 'science fiction.' Sorry about the confusion.
