What are their arrangements with the Nats? Do they get paid when players rehab? I know the players tend to go elsewhere due to the general conditions at the Pfitz but with modern facilities, i'd expect that to change. They really pack the place when there's a rehab start. Combined with whatever the Nats pay them (if at all) that should add up to a nice chunk of change. Obviously not millions, but a nice bump.
I'm not privy to their arrangements. But I agree that for sure their revenue would take a jump, though more than double seems quite a reach. They would also have a venue that they could potentially host other events like concerts. But that's peanuts as compared to P-Nats.