I was able to figure out a way of playing an incomplete version of the game from within the demo a little while back. It's a bit of a hack to get it working, and it needs files from the final game - so not entirely accurate, but it's still kinda interesting! I've added some (incomplete) findings to the page started by sourgrass.
For anyone super curious, the first byte of column F in John2022's sietch structure is used to determine when a sietch can be discovered. For example, Tuono-Tabr is set to 02, so when the game stage variable is 02 (which it is when Leto orders you to find the stillsuit maker), the sietch becomes discoverable. The game stage only goes up to C8 (I think), so those locations set to FF are revealed through other events.