1. The hyperspace map is well charted pre-collapse
2. System map is not charted if you have never been there
3. Sensor mechanics exist
I don’t even know what you are trying to suggest. There are already two layers of fog of war (2. and 3.)
1. Even if the map
was well charted pre-collapse, space isn't static. It is literally expanding and stuff in it moves, so long as the laws of physics matter (which, considering how the game treats black holes and some other stuff, physics aren't exactly real life). But I will grant you that no star system has probably moved a statistically significant amount in 200 years, assuming only laws of physics and no sci-fi trickery/AI nonsense. Plus, it's probably safe to assume that there are probably at least a few astronomers that still exist in the Persean Sector.
2. Buuuut, assuming astronomers exist, you can still figure A LOT of stuff out given time and a powerful enough telescope (radio, normal, infrared, take your pick). Or a scavenger might have already visited that arbitrary system and "charted" it (though admittedly the game so far doesn't allow a player to buy charts of unexplored systems). So don't tell me that a system hasn't been charted if the player has never been there, just not charted by player (game bounties will at least tell you something about a nearby stellar object where bounty can be found).
3. Sensor mechanics don't tell you c rap about a planet until you visit it (well, it used to, but that part of game seems to have been either dropped or skill-locked). So not all sensor mechanics are created equal. But admittedly, sensors probably do not pierce dimensional barriers (or whatever hyperspace is).
4. Considering that this game is to some degree just
JEWS Sid Meier's Pirates
IN SPACE, I agree that having some type of fog of war on the outer unexplored parts of the hyperspace map would be valid, although would be nice to also have options to occasionally "purchase" (money, quest reward, battle victory lewt) fogged parts to reveal them so you don't have to literally visit every part of the damn sector to get rid of the fog of war.
4a. If you don't get the Jews in Space reference, this will help:
https://youtu.be/ZAZhtT-dUyo