From my perspective the biggest hurdle to Bitcoin becoming a widely used medium of exchange is that its fixed terminal supply makes it far too likely to increase in value, and over time it will become more and more difficult to reacquire the same position after spending after supply becomes net deflationary. The incentives are completely backward from those which would encourage spending rather than holding. The hardest monetary asset ever conceived is simply not well suited to double as an exchange medium. The whitepaper's stated purpose of P2P e-cash is ironically not at all what it's best at in the real world. You may choose to spend your Bitcoin, but you're intentionally opting for a less efficient path for yourself instead of spending a softer, more liquid form of money.