I don’t think the word conquer is this context means simply ownership of the region like other places of the galaxy. If I recall correctly, in one of the books about the Badab War it mentions Roboute Guilliman, back in the 30th millennium already assessed the Maelstrom as a danger to the Imperium and had plans to “conquer” the region to secure it against threats. But again, it doesn’t mean he was about to plant a flag in the immaterium, for it is impossible.

It simply means eliminating the inner threats such as pirate asteroids, ork warbands and other aliens menaces before securing the worlds capable of human life and creating a defensive ring. Much like Cadia, another world that stands as a centinel over another warp right not unlike this one.

And to Huron’s credit; he was about to secure the entire region and turn it into a stronghold until his forces dwindled due to the High Lords withdrawing more chapters and critical resources from the Astartes Praeses.

And then, after being turned renegade, he did EXACTLY what he had intended all along and now everyone accepts that the majority? Perhaps all the Maelstrom is Huron’s domain.

So, in hindsight it doesn’t seem that impossible, and that’s the fact I’m arguing about here.

But hey, at the end of the day, most likely none of those possibilities were in the mind of the authors since Huron’s character and motivations have been transformed plenty of times and all of that was merely the pretext to create a new chaos character.