the only challenge that i can think of which really matters is adoption. and that is not something you can fix, it is something that is fixed on its own with time.
as time goes by more people find out about bitcoin and more of them start using it. some are merchants and some are users and they all make the ecosystem grow.
I agree with you. Even though the bitcoin is becoming more popular currency around the world but not all countries are accepting it as legal currency that could be used for paying goods and services. Another challenge is that bitcoin isn't user friendly. If only bitcoin is very easy to use, with just touch of a button, more less tech-savvy consumers will be interested in the world of bitcoin.