Apple should relaunch the original iPhone for nostalgia. No one's even paying $50 for a new iPod model. It will be nothing but extra burden to carry a device to listen to music around when you already have a phone.
Surprising that Apple has decided not to kill the iPod touch. That said, it is nothing but a stripped-down iPhone without a SIM card capability. It is identical to the iPhone 6 (if not later) otherwise.