Well... Today I went down to Best Buy and tried plugging my 12.9" iPad Pro into one of their shiny new MacBook Pros. The ones with ONLY USB-C ports.
I used the Apple Lightning to USB-C adapter that I use with their fast charger. The one they claimed would allow faster transfers, but only with laptops using type-C ports.
Anyway, I plugged it in, pulled up the system report and... It listed the iPad as only being connected at the normal USB 2.0 speed of 480mbps.
So FU to Apple. They don't sell any cables capable (or rather allowed) to connect the 12.9" iPP to a Mac at higher speeds than USB 2.0. Period. We can all stop trying to find the right adapter combination because the cable itself is crippled. The best we get is a USB 3.0 card reader.