IOW - the device becomes 30-50% lighter (on its own), and the buyer determines how heavy his/her experience will be based on which Qi-pack [s]he has chosen to run their phone
Want a 10,000mAh battery? No problem!
Want only a 2,000mAh battery? Again: no problem!
This even solves a problem Apple has let other vendors 'solve' with regard to cases - want an OtterBox? CrayolaCase? SiliconSoftie? Go get your case from any of a thousand manufactures
Apple could provide a pair (or trio, etc) of Qi-packs for their devices, and let other manufacturers go banana pants coming up with other options
This modularizes the iPhone in a smart way (not like that goofy Motorola method (which was reminiscent of IBM in the 80s open-standardizing the buses for their Personal Computer) whereby the only thing you "have" to get from Motorola was the core module
Apple's "core module" with such a program would still be iPhone ... and that is still the biggest differentiator Apple has vs the 80 scadzillion Android makers out there: iPhone is only Apple. Android is whomever wants to make one.