Bitcoin doesn't solve the problem, because you then still need to solve the "how do you convince people to buy the Bitcoins when they can just use a credit/debit card" (you can get pre-paid MasterCards in convenience stores across the world) and the "how do you actually get people to buy the Bitcoins" problem - the answer to the latter currently seems to be (a) buying it off some slightly disreputable website that you find by asking on Reddit, or (b) localbitcoins, where you agree to meet some random person in a car park or shopping centre and exchange cash for BTC. Not shady at all.

Bitcoin and cryptocurrency literally solves nothing in the app payment use case.