We basically had the idea in discord to have small pockets of the map be inaccessible until you defeat a "fortress sector." where the enemies are more numerous and maybe even contain a randomly generated boss or something.
Once the sector is cleared, the pocket will become accessible via jumps.
inside this small pocket might be an enemy HQ, better drops, a high concentration of claimable asteroids or secret stashes, etc. Things that the player would like.
Accessing a fortress sector would be done by a special gate that tells the player it leads to the fortress sector. You cant directly jump into it until its cleared. Afterward the player clears it, the rift/wall around the small pocket would disappear allowing hyperspace jumps in and out of it. Some kind of map marker or color would remain denoting which sectors are a part of the hidden pocket - maybe even just automatically get tagged as "secret space" with map tags.