I think that hollowed out asteroids in the main belts would add a new flare to PvP/PvE.
A ship sitting in a hollowed out asteroid would be undetectable to scans and probes but you could be able to use probes to scan down the system with.
The only way that the other ship would be able to detect your presence in the asteroid is based on your movement, as soon as your ship moves you become visible on their overview or if the ship happens to close to the opening, 5km and conducts a scan.
The hollowed out asteroids would span in different systems after each downtime to ensure a random variable is present.
The hollowed out roids would provide interesting ambush scenarios for PvP and PvE’s alike.