https://developer.apple.com/LIBRARY/...roduction.html
The os is not fully 64bit according to this but has 64bit libraries that allow apps to run. But this would definitely be like you mentioned earlier then that they have two distinct os's to support the models of phones.
So now they are pressing to have apps converted to run 64bit as there are some issues with the 32bit crashing.
Apple A7 processor and iOS 7 causing more apps to crash | Digital Trends
Overall they have to pick one and go full out for it to perform 100%. This should be soon, but guaranteed android is already on this road and will probably have it done soon.
And we can only hope blackberry has been looking into this with how qnx can run different os's on it, that they were thinking about 64bit when they were going for os10. They would be crazy to just work on the one without looking further.
BlackBerry forever, haters never!