The number one problem that is being worked on endlessly across all cryptocurrency devs, regardless of their goal, is... simplicity. It's somewhat infuriating that, with all of the complexity involved with cryptocurrency, and all of the problems that it solves in today's exponentially growing financial world, the missing piece is to make it all EASIER to understand than paper money. The moment someone figures out how to explain cryptocurrencies in a basic way - the same way you explain what "money" is to a child when they are growing up - is the moment cryptocurrency will skyrocket like we've never seen before.
People fail to understand (especially those involved in technology) that today's society, and certainly the society of the future, is not open to change the way it works so drastically (from "money" to cryptocurrency) without extreme benefits that can be summed in a few sentences. It has to be as simple as "which do you prefer - $1 or $100?", money versus cryptocurrency, respectively. We are certainly not at that point, or anywhere near it, no matter how large the cryptocurrency market is.
The moment you are able to convince and prove to the world that cryptocurrency is undoubtedly better than "money" (cash, debit/credit cards, banks, whatever) is the moment the entire world's financial systems will change overnight.
Some really good points in there Stolarz! The perception of what cryptocurrency really is to anyone outside of the cryptocurrency industry is still really muddied - and that comes down a lot to a lack of transparency and good education initiatives being created.
Right now we're going through a generational change as well where millennials have spent much more of their lives with some knowledge of cryptocurrency at least. In the coming years the habit of using physical cash will become less and less common, and naturally peoples' understanding of virtual currencies will improve also.