From what I've seen, airlines account for their point liability in a number of round trip tickets. I believe the average liability incurred across the industry is $64 per ticket.

About 75% of points get redeemed (since people who get a lot would tend to use them), so the total cost of a ticket if everything was redeemed might be around $64/.75 = $85 USD.

Seems like tickets range in cost, but 50k seems a fair estimate of the average flight (probably a bit high). So $0.0017 per mile incremental cost (higher opportunity cost).

This INCLUDES all the people gaming the system right now, though. And Avis is paying the airline for the points, so the airline wins no matter what happens — it's a billion+ dollar profit center for them. Avis might be a bit more annoyed.