Science fiction themes tend to be cumulative in the sense that themes come to science fiction and after a peak of interest and experimentation tend to settle down to a steady turn out of new stories. Think space opera, cli-fi. cyberpunk, alternaivte history, new wave etc and how they never really disappeared. They're still with us on tick-over.
With so many themes joining science fiction and the inevitable mash-ups between such themes, it may look like a spaghetti mess of old stuff to many people. The greater spectrum of what already exists weighs against any new themes that could come along, just be looking at the numbers of sub-genres. As for new sub-genres to come, maybe:
- gene-ism – the impact of altering genes in the human, fauna and flora species
- engineering impact – the ability to alter our surroundings to make our lives more interesting or easier (this differs from science impact because it takes into account the practicalities that need to be dealt with in the story one way or another)
- life-differentials – with the difference in life-spans becoming ever greater for various reasons, how are people going to react to each other and why
- habitat influencing – where the habitat for humans changes and how their physical and mental well-being are affected over the generations
- quantum physics impact - there have been tentative forays into this subject, but it still needs to be grappled with in depth and via nuance.