I'm not sure about 2018, but by 2020, absolutely. I think you'll be able to spend bitcoin at mom and pop stores before the big ones to be honest.
There's a lot that goes into directly accepting crypto payments, so most people who do use a third party, which adds an extra layer of fees and processing. Makes me think that either Amazon is going to roll their own blockchains soon, or they'll be buying out a company like CoinPayments for easy integration.