Digital Foundry says $8, and they’re as well informed about this as anyone saying anything publicly will be.
If I had to guess, I’d assume that this has to do with discounts. A large proportion of AAA games are not bought at full price.
I see where your 11 games estimate is derived from, but it’s worth remembering that this includes games that are digital-only, i.e. they get the same money from both console editions.
The only way I could see a deeper subsidy happening is to kill the second hand market / lending games to friends, without getting the xbone backlash. I think in the end I bought 5 or 6 games on the PS4, and played another 4 on disks borrowed from friends.