Seems that Iphone is the first to get the 64-Bit CPU or something and in the future, the Android devices will be next for next generation mobile performance. There may be 64-Bit Windows tablets but that doesn’t count as they are the same kinds of tablets ever since the past ones like they are not 100% as mobile as the Ipads and Android tablets are.
Having 64-Bit CPU in a mobile device may give you the experience in making use of more hardware resources such as the full RAM usage for example. The first Android device will be the HTC Desire 820 which is like superseding other Android devices as HTC is like on life support nowadays due to Samsung taking over the Android market by storm.
Further announcement will be happening in September 4th or later as part of the upcoming IFA event.