Except that you could use it in apps from the start? Device to device sounds great, but that's not close to how Apple Pay works (standard credit cards, not merchant accounts). Square and others now simply provide NFC readers and it works fine.
But it'd only be Apple devices that can pay at that point, so not really worth it.
I had that thought when Apple Pay was first introduced last year. Seemed like a no-brainer, especially since Apple doesn't mind doing the walled-garden thing.
Unless Apple plans on opening a bank, the limiting factor here is still that you/your buddy will be taking a haircut on the credit card processing fees.
Apple Pay doesn't replace the card network, and the card networks are NOT interested in being structured to be micropayment friendly.