I don't see why reserving PoBs to being SRP-only wasn't implemented in the first place.
Edit: And genuinely, in most cases there's very little that any faction that isn't a House Military can do about shielded, supplied bases. Take Gallia for example. Multiple bases in the Maine system alone.
None of the unlawful factions can do anything about them. Corse and Council wouldn't want to attack them due to their tenuous diplomacy, Brigands don't have the firepower, and Maquis can't even use Gunboats.