You got a good points there.
All of us - the people present on this forum all know Bitcoin and all coin famous.
But I think the future development of digital currencies to replace banknotes or banks depends greatly on one of the following factors:
1. Qualifications and knowledge of the people. Because the majority of people today do not fully understand block-chain and technology. So if you want to use cryptocurrency like paper money today, all people have to know how to use technology
In order for a certain technology to propagate, there should be a widespread information campaigns and seminars. This may take sometime and a huge amount of budget but I believe it worth it. The question is who will be the one to do such task.
2. Smart phones - Must be integrated with technology to make it convenient for people to use
Smartphones.. yes almost every capable teenager wanted to have a mobile phone. Having technology integrated in this will certainly brings this technology nearer to the prospected audience. Mobile phone is one strong tool for adoption.
3. Simplification of cryptocurrency developers. How can people easily use like paper money.
There is nothing more annoying than a non-user friendly apps. One of the reason why most invention failed because they failed to make them user friendly.
I could add one more, government acceptance and support. Anyone can create great idea, technology and inventions but without government acceptance and support it will be a hard road for adoption. The government saying yes is like a house with open door which means, adoption, development and adaption will be much easier because there is someone with stronger power will support the project.