I've sat out two upgrade cycles waiting on Samsung to come up with a viable replacement for the S5. I want a battery that can be replaced by mere mortals. It doesn't have to be as easy as the S5 to do so. But, it needs to be replaceable during its lifespan without sending it off to timbuktu.
Seems to me the whole exploding phone business wouldn't have happened had they not been bowing down to the god of thinness. S5 is a great form factor. Why do you need it smaller?