You seem to think a SfY app on a different platform would not be taken down. Apple took the app down after a simple letter from the patent holder. The patent holder could have asked for relief in court, enumerating the infringing apps. IANAL, but that's a common request in patent cases, and usually granted by the court. All app stores would have to comply then, however free (or non-totalitarian), maybe even removing the already installed apps.