I played the demo, and the only thing I was really really missing was a map. Are there any plans to add a metroidvania-style map with some sort of pointers? My friends, who have already bought the game,say that they're having the same problem I had in the demo; they can't quite figure out where to go after flipping a switch/opening a door/passage/etc. Except now it's a fool game. I feel like if it hindered my progression in the demo, it's going to be much worse in the full game.

There are no plans for that as far as I'm aware.

From what I could gather from various interviews with the devs the game was actually designed from the ground up with no map feature in mind. Which, imo was also the right decision. You're this amorphous blob of teeth, flesh and tentacles and navigate primarily by instinct and primordial desires such as survival and hunger after all.

In my experience (finished the full game twice now) there are one or two sections where you can get a bit lost but those ingame screens or billboards keeping track and showing your progress for the different zones and the creature's roar/echolocation ability (showing the approximate location of the next/nearest save point) definitely help getting you on track again.
And the individual zones/levels aren't that huge and sprawling as they might look like at first to begin with.