I don’t think this will happen, but Apple has been granted a patent that shows an iMac with a recharging slot of a removable battery for an iPhone, iPad, Magic Keyboard, and Magic Mouse. The patent (number 20170200988) is for a “battery charging system and mobile and accessory devices.”
It involves a method and system for recharging batteries for wireless electronic devices. The system includes a host machine — that would be the iMac — providing charging slots and wireless devices coupled to and powered by a batteries.
In the patent filing, Apple notes that an “apparatus or method” is needed that can that can reduce or help users manage the power requirements of the plethora of wireless devices. The company says it would be helpful to have an apparatus or method that can reduce the time wireless devices are taken out of commission as their batteries are re-charged and that it would be helpful to have an apparatus or method that streamline the process of charging the wide variety and number of batteries used in the plethora of wireless devices.
Of course, Apple files for — and is granted — lots of patents by the U.S. Patent & Trademark Office. Many are for inventions that never see the light of day. However, you never can tell which ones will materialize in a real product.