Re: Opportunity to get rid of 32bit silicon?
I'm willing to bet Apple is getting pretty close to dropping the 32 bit ISA from the iPhone/iPad SoC. It is only needed now to run apps that haven't been recompiled since before iOS 7 was released and universal apps could be built. Seen in the light of Apple's recent announcement that they will soon start housecleaning apps that haven't been updated in a long time (they haven't specified how long) makes me think that in either fall 2018 with the A11 & iOS 11 or definitely by fall 2019 with the A12 and iOS 12 Apple will:
1) build that version of iOS 64 bit only
2) drop support for the remaining 32 bit hardware (iPhone 5 & 5c, and iPad 4 is the only 32 bit hardware iOS 10 supports)
3) drop non-universal apps from the app store (i.e. those that haven't been built with the new tools that came out with iOS 7 back in June 2012)
The apps still on your phone that are 32 bit only could still be run, as it is easy to emulate the 32 bit ISA using a 64 bit CPU (Apple did much the same thing for its various transitions in the Mac world) but they'd be gone from the App Store, so if you deleted them off your phone you wouldn't be able to re-download them.
Doing this would have a lot of benefits for Apple in reducing the effort involved in designing and (especially) testing new versions of iOS and new SoCs, since all the 32 bit stuff simply goes away.