I posit that the next generation Smart Keyboard therefore will ship with QI charging in some form to enable powering the iPad during use via the Smart Connector.
It is perfectly possible to charge an iPad via the smart connector (http://appleinsider.com/articles/16/04/30/review-logi-base-smart-connector-charging-dock-is-the-best-way-to-juice-your-ipad-pro), this specific product lists an estimated 7 hours to charge the first generation 12.9” iPad which isn’t blistering fast by any measure.
Early indications are thatApple may not support the QI Extended Power Profile (http://pocketnow.com/2017/08/27/iphone-8-may-not-support-qi-at-15w) which would mean only delivering 7.5W rather than 15W for the iPhone 8/8 Plus and X. If this is true, and I have thus far been unable to find a clear answer, it seems likely that the iPad would rely on the charging capacity.
15W would be sufficient to charge the iPad slowly during active use, after all the current iPad ships with a 12W charger which works fine, if a bit slowly, in this scenerio.
7.5W however would probably be sufficient to sustain the battery at its current charge pretty much indefinitely at most common loads, or at least extend battery life truly all day regardless of use. For some real world data on charging the iPad at different wattages and loads MacStories has some in their excellent review of Apple’s 29W USB-C charger (https://www.macstories.net/ios/testing-apples-29w-usb-c-power-adapter-and-ipad-pro-fast-charging/).
The implication would be a portable device which you can use for serious productivity work without compromising on computing power, which works as if it was plugged in. Put it down on any coffee shop table or any office desk in the near future and it will automatically never run out of power. Unlike the iPhone, many more use cases remain available while charging and therefore I suspect wireless power will remain a convenience for iPhones but a powerful enabling force for iPads in exactly the use cases Apple are pursuing for the device.
While not true wireless power, which would fuel your iPad while you sit in your sofa, this likely has the potential to be good enough to be magical for a surprising amount of people.