To be clear, we allow issuers and acquirers to come up with bilaterals and we will support them. So they're free to enter into a completely private arrangement, and our technology will support them.
But we're not telling the acquirer, this is what you have to charge; we're saying, this is how much that card transaction will cost. What you mark it up to is entirely up to you, acquirer.
I just want to correct one thing. Interchange is part of a revenue stream; it doesn't determine a margin. An issuer might have to spend that entire revenue stream to cover loan losses, chargeback liability, and rewards benefits. And grace periods are funded out of that as well.