You won't get the developed world to take an interest as a currency, rather only as an investment.
The developing world doesn't have credit cards. They also are interested in $5 a day in extra income.
Did you know filipinos spend more feeding their pigs than they sell for thus no profit? Yet they still raise pigs. Why? Because it is a savings account.
The world is getting smaller, quickly. As you say, Apple, Paypal, etc. are rapidly targeting the developing world. You have a few other such solutions there or going there as well, such as M-Pesa.
It still isn't clear to me that the developing world wants decentralized currency. Once the same or similar services from the developed are available there, consumers will likely make the same choices.
Credit cards are going away in the developed world too, or more properly becoming a speciality product for high end individuals and businesses. The mass market is increasingly debit, including the somewhat recent trend toward prepaid debit. In part because the masses are increasingly not credit worthy. The original point is valid for "payment cards" though.
And none of them are giving away $billions "for free" in $5 daily morsels to rocket launch the inertia.
Distribution is the key. How many times have I told you this.