Now that I think about it, having a fingerprint reader on the back like the superior Galaxy S8 is not that big a deal. In fact it's more ergonomic and convenient.
With the larger iPhone Plus, one handed use with the home button makes it semi difficult to reach the home button/awkwardly use your thumb in a downward motion. I could see the ergonomic design with the sensor being placed on the back being useful for some for larger phones. I do think I could adjust to the Touch ID sensor on the back of the iPhone, but it would take some adjust and it wouldn't stop me from purchasing it.