This would be fun on a single player universe and introduce some story based gameplay somehow.
On multi player the technical aspect of it simply might be prohibitive as others have said.
Scanners should be able to identify undiscovered stations within range of the scanner, in fact this is what I thought they did at first! There would have to be a caveat to that and in the case of pirate stations, the scan should be detectable.
Again, where this data is kept would dictate whether this could be achieved multiplayer. Maybe a "known" universe file could be built up as players travel through systems and carry out scans. The scan data could be available from the navigation menu and a decay value applied to it so automatically purge it. So if someone travels far from spawn, their trail would be captured by this file, but then as time passes, if nobody travels there again for a fixed amount of time this data is slowly erased from the file until it is gone. Spawn and the 8 systems surrounding it may always be pretty full of data but as you move away, the data will become less. Maybe some financial or artifact based caveat could be applied to the quantity of data that can be displayed to the player.