I see your point but I still believe anything with a A6 or lower will be dropped. If you look at that chart, assuming it's somewhat representative, the vast majority of iPhone users are on A7 or higher CPUs. A7 up are all 64bit. This is the same company that released the first Intel Macs in January 2006 and OSX stopped including PowerPC support in August 2009 with Snow Leopard. About 3 1/2 years.
The last 32 bit CPU was in the iPhone 5, A6, and introduced September 2012. 64 bit A7 in September 2013. By September 2016, I could totally see 32 bit being dropped after 3 years of dual support.
Hey, it's just my opinion, but I always look at past history to look for patterns. Apple is also notorious for trying to keep teams small and not waste resources. I don't know if you remember the stories about the Apple remote app not getting updated because the one developer who wrote the app was working on other projects. Why keep a team working on 32bit OS X when you don't make any new devices with 32bit CPUs and haven't for quite some time.
It just seems to be a lot of circumstantial evidence.
Like I said though, just my opinion.