The Dune analogues throughout make it seem like the Tanks are the way the Inchoroi or Dunyain women went.
We sorta know how Inchoroi reproduction works - they're a single-gender species and the Ark is their womb, hence Seswatha calling them "the orphans" and the Ark a "dead womb". So their mothership is literally their mother, the female of the species, while also being a self-sustained biosphere. Think of the Inchoroi as white blood-cells that can survive outside the body, or honeycomb produced by bees (the Ark being the bees, not the hive), or even the mitochondria born inside cells.
I imagine their species works a lot like the aliens in Peter Watts'
Blindsight, who are a part of their mothership's ecosystem and don't exist "independently" from the alien environment that birthed them.
But then again, me and you don't exist "independently" either.
Were do you draw the line between organism and environment? The thousands of mitochondria living in our cells are pretty much organisms in their own right; they just need the cell's environment to survive. The human body is the same; it's "self-contained", has its own reproductive ability, but needs an external biosphere to survive at all. How does that make us "individuals", while our mitochondria are just "organelles"? It's nesting circles all the way out. Any coherent definition of "self-reliant individual" will just keep receding to the horizon until you basically have to call the whole biosphere a single being.
Its not a huge stretch to imagine that the Dunyain women could possible be used for only breeding purposes, but I dont think so.
I have no idea either, and my guess is as good as yours. But from the evidence we've got, I think it's pretty likely that the Dunyain went that way.
Also, there are a few references to Dunyain women, at least tangentially.
But they're very tangential. Not a single reference to a female Dunyain individual back home. Not a single reference to Kellhus' mother. Does he even have one?
When speaking of world-born women baring his seed, its definitely implied, if not outright said, that only true Dunyain women care bare functional Dunyain children. There are women, we know they breed with the men.
Well, yeah. I don't doubt that
females exist in Ishuäl, since the Dunyain clearly reproduce like we do. However, we have no idea if the women are just breeding stock, reduced to brain-dead Axolotl Tanks for maximum breeding efficiency, or if they're actually
persons that the Dunyain think of as mothers and sisters.
I think its equally as likely that the women are the superiors running Ishual, the Bene Gesserits toying with their puny minded men, sending them out into the world to die, rather than the opposite Tlelaxu analogue.
Bakker-world being what it is, the most misogynistic path will usually be taken...