What would convince you as a consumer? If everyday products were 3% cheaper, would that impact you at all? 5% cheaper? At what point do you think people would care? What about cash only businesses? As a consumer would you prefer if you could use your phone instead of pulling out and handling cash?

If adoptions ever takes hold, I think it is unlikely to start with the replacement of payment cards. It is more likely to take hold is specific niches that currently suffer under the MasterCard/Visa duopoly as well as in emerging markets. In the adult industry, I'm sure products being 20% cheaper would sway consumers. Also not to mention the omission of purchases from your credit history which may be judged harshly by others. Low margin businesses could support online and international sales while offering competitive prices. Some markets aren't serviced well by the duopoly. Some consumers value pseudonimity/anonymity in their financial transactions. These can develop into niches where crypto has potential to take hold, and then from there it might expand and compete with the larger markets (and their vigor) if it grows into a competitive product based on fees and usability.

If it ever hits critical mass, vendors will surely either drop card support or strongly encourage cryptocurrency usage. Albeit that is a big "if" that likely comes down to solving a lot of scalability and usability issues right now. There is also a need for regulatory clarity. I think we are a long way away, but I wouldn't write it off simply because I personally find Visa/MasterCard to be convenient in my own life.