I think iPhones will stick with Lightning until wireless charging is fast enough that Apple can remove all ports, Apple Watch-style.
In fact, I don’t think regular (non-Pro) iPads will switch to USB-C either. Apple is pitching the iPad Pros’ switch to USB-C based on actual professional features — driving external 5K displays, using PC-class peripherals, and support for very high-power charging. The only one of those that might apply to regular iPads is faster charging, which is always nice to have, but even that wouldn’t matter much to most iPad users, who (a) stick with whatever charger Apple supplies in the box, and (b) choose extra chargers based on price, not output wattage. (Spec-knowledgeable nerds have trouble believing this, but many iPhone users love the wimpy 5W charger Apple includes with iPhones because it’s so small.)
I completely agree – the way the Apple Watch charges wirelessly-only and the new Apple Pencil charges wirelessly, would seem to indicate a wireless-charge future that Apple sees for their mobile devices in future. A future iPhone without a lightning port (or any port) would allow them to design an even thinner iPhone.