It what sense is bitcoin a direct competitor to Apple's rules on purchases? If, as is repeatedly stated, bitcoin is a legitimate currency Apple could choose to support it for purchases -- and still charge a 30% fee just like they do other legitimate currencies like British pounds, Canadian dollars, Mexican pesos, etc...
If you think allowing bitcoin wallets on the App Store meant devs could offer digital purchases on iOS native app via bitcoin and avoid Apple, both the selling app & bitcoin app (or British pounds or Mexican pesos) would be banned for violating TOS.
If you think an iOS dev could offer a digital sale via web, in any currency, that can be downloaded on an iOS native app and avoid Apple's 30% - they can do that now. Kindle books, Comixology books, nook books can all be purchased via web with no fee to apple, but can be downloaded in the various apps on iOS.
Bitcoin hardly needs Apple's approval to become a true currency. Apple is not known for it's leading the pack on these kinds of issues.