bitcoin can also work as a niche thing imho, i don't see the problem with that, maybe not forever because miners need an incentive in the future to keep mining with a smaller reward...
Bitcoin is too great an idea to have just niche applications. It is still very young, but has got the imagination of millions of people. If you compare it with technologies like telephones or internet, adoption has been much faster. I am sure you will see adoption increase quickly with time.