The Xperia Z4 can perhaps be considered a blotch on Sony's troubled mobile reputation. It was an incremental upgrade at best and an overheating catastrophe at worst. Even Sony implicitly acknowledges it's only a small step forward, naming it the Xperia Z3+ outside of Japan. While very little can be done to salvage the Xperia Z4, Sony's redemption might come from an Xperia Z5 slated to arrive this September. And based on some recent rumors, this one might actually be worthy of being called a flagship smartphone.