Two years from now, merchants won't be paying 3%.
I am pro bitcoin but, I am very skeptical of the frequent claim that bitcoin will enter mainstream usage without fees similar to that of credit cards.
Others will pay a small fee for the convenient that a full-service solution provides. Right now, bitpay charges 0% and a small monthly fee for payment processing. To be honest, I see them staying with that business model, perhaps permanently.
If they or other incumbents start jacking up the fees, someone else will take their place. Bitcoin community is swarming with entrepreneurs.
If you run a SaaS company and your Pro service level costs $20/month, would you change your price to $19.40/month if you were able to eliminate credit card transaction fees? What if your service involved a little bit of manual data entry by your employees every month and you found a more efficient way to do that; would you reduce your monthly fee by the effective cost of the few seconds a month of employee time you've just saved? Perhaps drop it from $19.40/month down to $19.37 a month? Of course not. Whoever signs up for your service sees value in paying $20/month and they honestly don't care what your underlying fee structure looks like.
Merchants just charge everyone a little more, and nobody cares.