They've also built a bit of an ecosystem of Lightning-based accessories—AirPods, the Magic Trackpad 2, the Magic Mouse 2, the Magic Keyboard, the original Apple Pencil, the Logitech Crayon, all the random non-Pro iPads, and the Apple TV remotes. Besides controlling the connector for $$$, I wouldn't be surprise if a move away from Lightning might be more disruptive than the move from the Dock Connector to Lightning for some people ("They're always changing the connector!")
For me personally, it wouldn't disrupt much since my iPhone charges via Qi and I'd just need a USB-A->USB-C cable for the car. Everything else would still be Lightning and it would just become my "iPad and Apple accessory charging cable."
If I'm guessing, the entire iPad line moves to USB-C first, unless the EU mandates that Apple change future iPhones. There's a lot of possibilities regarding the EU, as there's talk that it might just be concerning the chargers themselves, or if you can use an adapter, or if the device itself needs USB-C. I kind of wish they had thought of the outcome first, but we'll just have to see.