I think we can all agree that Safehold and HoH/Pardal were parallel stories. Cool, standalone stories, but very related themes.
But there are a TON of threads that are hanging out after HoH:
- the commitment to free the Achuultani
- more planets in the
- pre-historic non-human empires
- humanity's true home-world (Mycos)
- Pardal's integration with the empire
- The "next great discovery" hinted at in HoH
... the list goes on
Then there's the Dahakverse itself -- where a lonely Utu class starship couldawaken to find itself aware of itself. There may have been thousands of them at one point ... is Dahak the only one that is self-aware? Or, did this happen a few times, and so horrified the Imperium that they vowed to prevent it from happening again. Would self-aware starships fled to far flung stars to save themselves?
The story of how the bioweapon was created and unleashed could be told. Did they actually do it to themselves or was it hastened by an outside element. We know how it ends, but how did it begin?
What if the nest killers come back? What so terrified the Achuultani that they fled their galaxy to escape them?
It's a rich field.