Confirmation speed, transactions per second, volatility, non-reversible payments, and absence of credit... not there yet.
I love the idea of non-reversible payments, but it represents a major transition for consumers. Consider the most successful Bitcoin markets, black market sites, and their reliance on escrow. Although reversible payments can be a source of fraud, they are
also used for consumer protection. I see the fraud limiting aspect of non-reversible payments benefiting sellers more than buyers. Mass scamming is incredibly easy for merchants, in absence of consumer protection. FE (finalizing early: releasing funds from escrow before the exchange of goods or services has been completed) has been a cornerstone of fraud in many marketplaces.
Credit is also valued by many people. It is out of philosophical alignment with the Bitcoin community, but not the majority of consumers.
Affecting cultural change is just as vital as making technical improvements. Bitcoin also does not have a stellar reputation, yet, and that is part of the change that needs to occur.
Beyond just '
can Bitcoin replace X?', clearly explaining
why Bitcoin is better than X is necessary. Libertarian platitudes do not hold widespread traction.
Does Bitcoin offer a better end-user experience
than a Starbucks mobile payment app? Mass adoption includes those users.
I think Bitcoin has potential to be enormously successful---without immediate need to overthrow and replace alternate payment systems.