Keep in mind the nature of fiction. It has an obligation to create friction and conflict. Intrigue is built into a fish-out-of-water story. Reality is far stranger, and far more complex. People and culture interact in imperceivable ways, and our influence on each other isn't something we can predict. Nor is one type of culture drift good, or another bad. It isn't better or worse in reality to have concetrated pockets of similar-thinking communities. In fiction, it is narratively expedient.

We don’t have pockets of cultures, we are steadily pushing toward having a single culture, a mass of haphazard associations and little comprehension of meaning.

Kinda true on the push, but not on the "we don't have pockets of cultures". Lemmy and the fediverse as a whole can be described as a pocket of culture, maybe a subculture of a larger thing. It doesn't matter how hard the corporate overlords try to impose a single culture, people within it will want to subvert or change it one way or another.

I’m talking about how pockets and islands of cultures pop up everywhere within these settings,

In real life, this happens with cities that receive many immigrants or after any diaspora. People from far away always bring something with them and, depending on how they are received and integrated within their neighborhood and society, some changes will show up, given time.

Lastly, schismogenesis is a real thing - cultures can form entirely out of "we are DIFFERENT from them"

I don’t think we’re heading towards a monoculture. Actually much like Cyberpunk, you’ll find the most striking pockets of unique cultures in small spaces relevant to whatever group is there. Go to a skatepark and you’ll think the people there are talking another language. Go to a concert or rave and you’ll see all kinds of different subcultures and fashion styles depending on what kind of music is playing. Even here on Lemmy you see different cliques and subcultures. There are astrology conferences and Beyblade tournaments and everything in between. Theres also always little pockets of ethnic groups, foreign to where they are, all over the world. I love finding different groups and the things they orbit around and the lingo they develop and the ideas and values they have. They’re not as easy to find as they are in a video game, but they’re out there and it’s a much more rich experience to get to know those people than in a video game.

I can’t describe it well because I’m not an anthropologist, but the changes in the larger zeitgeist over the years I’ve been around seems to be pretty normal too. I don’t think there’ll ever be some kind of monoculture, just that what makes groups different will naturally change over time.

Haven't read Neuromancer in a while, but didn't the rich have private satellites?