I get why some core apps are not deletable on iOS. Accidental deletes happen. Not everyone goes to the App Store. Not everyone has a constant network connection. But third party apps should be deletable.
I don't think Apple would spend $$$ on developing a third tier version after the 6/6+. I see them perhaps re-casing the 5S with a better cam but not put the rest of the internals on par with the 6 or 7.