Big, big money
Establishing a competing payment system to challenge MC/Visa seems akin to taking on the Comcast/AT&T duopoly - prohibitively expensive and with such a regulatory obstacle course than only an entity on the scale of Google or Amazon could really make a go (Google Fiber).
Even PayPal and Square can be pricey for small businesses. On the downside for cybercurrency, however, are the sometimes wild fluctuations. An SMB accepting payment for your sandwich in bitcoin can't be sure that next day, it really gets the full amount. Do you see any cybercurrency addressing that issue?