Just want to point out that some people are working their ipads/phones harder than others and it's best not to generalize about use cases.
For instance many musicians are running "audiobus" with separate sequencers, synthesizers, and effects all running simultaneously.
Still others are itching to run CAD programs. Personally, I would love to use Fusion360 on an iPad Pro with an A7X processor.
It's not hard to imagine that versions of Logic/Final Cut and other professional applications will soon arrive on iOS and that users will want to run multiple instances of plug-ins such ashttp://www.waldorf-music.info/en/products/nave.html
To claim that these users would see no benefit from 64bit processing is misleading in my opinion.
What about the physics and AI of ambitious games which are still typically calculated on CPU's?
It may seem silly but people are already using apps like http://www.native-instruments.com/en/products/traktor/traktor-for-ios/traktor-dj/
+ many others for live performance and in some cases to earn an income.
I think people are not yet accustomed to the pace that mobile is moving at due to the large amounts of money being thrown at it and the fact that most of these problems have already been solved in the past.
So it's a question of why not make the transition now to minimize the pain later?
There is a shift from consumption to creation taking place faster than most anticipated in this space and I think Apple are simply being proactive so that they can meet the demands some of the more hardcore users are placing on these devices.