I just picked up the new RavPower
here (not an affiliate link). Like others have said it says it will support fast charging (7.5w) for the new iPhones, whenever that update comes out. It actually supports up to 10w for certain Galaxy, Pixel, and Lumia phones too. I really doubt Apple is doing anything special so only the Belkin/Mophie can support 7.5w (like MFI or something). As far as I know, the wireless chargers just output their max wattage and the phone takes care of the rest.
I took a look at
https://www.wirelesspowerconsortium.com/developers/specification.html, which explains the versions of the Qi standard (what Apple is using). Airpower seems to be just a layer on top of Qi to support charging/battery information and passes that to be displayed on the phone. From the coverage I read about Airpower, Apple is working with the wireless power consortium to make Airpower work. It seems like a software layer, think AirPods + W1.
Side note, I chose the RavPower over the Mophie because it seemed a little less proprietary. The plug is a microusb instead of a non-module wall wart.