I guess they have good intentions but you can't simply make a phone have a replaceable battery since phones are tightly packed nowadays, you may have to change the way the phone is packaged quite considerably if the battery is not near the back of the phone.

Also whats the point of replacing the battery of an out-of-support phone? Even excluding Android being out of date some applications will not let you even connect to their servers if your application is too out of date.