250 million people isn't mainstream? These are people sending money to their families on a monthly basis, and where current transfer fees can take the equivalent of a half day of work.
a highly regulated one too, crypto does not address the complexities of international monetary regulations. If the solution is to not abide by the existing regulations, it not going to be mainstream.
As jogjayr pointed out, the Hawala system has existed before and after formal regulations. Crypto alone might not represent a viable mainstream alternative, but it does have potential as one piece of a composite solution.
That strikes me as an appealing use case.