The Wordsmith's Forge

When I want to create hopeful-ish stories, I tend to postulate technological humans going a bit crazy with biotech as their end approaches, making somewhat scattershot changes in their own descendants in the hopes of speeding up adaptation to their new environment, and getting human descendants into niches they'd have been unlikely to reach via blind evolution. Of course many of those changes prove unsuccessful or outright harmful, but it gives evolution more to work with among human descendants. And in an ideal world, the various strains co-operate with each other, allowing access to groups of resources none of them could get alone. Sometimes I even include small groups of original-style humans, living underground and maintaining as much knowledge and technology as they can. I don't think this is especially plausible, particularly the cooperation across descendant breeds, but it makes for a less miserable story.