I'm definitely on the crazy train. I believe Doomslug is a component of the cytonic hyperdrive, either as a backup for non cytonic pilots or as an actual complimentary piece to a cytonic pilot. I have a feeling that a human cytonic doesn't have enough power to move something with as much mass as a spaceship on their own and Doomslug's race is capable of cytonics. Of special note is that Doomslug mimics the humans quite a bit. I don't think Brandon just threw that in there. I think it's a mechanic of how the slug and the human work together to move the entire ship. Human moves themselves where they want and the slug moves the ship. There are also these WoBs:
Questioner
What does Doomslug eat?
Brandon Sanderson
Doomslug eats mushrooms, among other things. I don't want to say anything more...
Questioner
I know, I was trying to find something that wouldn't be RAFO'd
Brandon Sanderson
Yeah that's actually shockingly relevant of a question, so... Hmm!
Sciencetor2
I am subscribed to the, "Doomslug is the hyperdrive," theory. Can you confirm or deny?
Brandon Sanderson
I cannot confirm or deny.
So Doomslug was the reason the original pilot told M-Bot to collect mushrooms. Gotta keep your slug alive.