You can't process a Mastercard transaction over Visanet even if you wanted to: * The network won't know who to route the BIN range to * Even if it did, they may not be connected * Visa and Mastercard, although very similar, put different pieces of data in different places and have different business rules, so you're not necessarily going to have the information you need to process a transaction where you expect to find it nor is your processing of that transaction necessarily acceptable to Visanet. * Visa doesn't know Mastercard's PEK, so they cannot encrypt the PIN as the issuer would expect it even if they wanted to * The EMV crypto might not work, although I'm not sure

These are just the problems that occur to me off the top of my head. They are solveable, but it would require a decade-long regulatory commitment with serious weight behind it.