It has been recently reported Apple is engineering its own processors for the Mac platform. These chips will not replace the Intel processors used in all of the Mac computers.
It will enhance Mac deep-sleep functions where the Intel processor will not turn on for system updates or collecting emails when the screen is off or the laptop is sleeping and the lid is shut.
The Mx or Mxx motion coprocessor used in the iOS devices since September 2013 when it was introduced in the iPhone 5S on the same board as the Apple A7 System on Chip (SoC). The latest motion coprocessor, the M10, is located within the A10 SoC, which has been the case since September 2015 when Apple decided the M9 should be on-die with the A9.
The coprocessor Apple is rumoured to be developing will not be a motion coprocessor. It will be similar in the way it is developed, but its functionality will be very different to the motion coprocessors.
Apple employees have been working on this project for a few months to a year. Judging by the timeline of normal releases and when leaks occur, the development of the first coprocessor is complete and is likely to feature in the 2017 12-inch and 15 inch MacBook computers alongside the Intel m-core processors.
If you would like to find out more about this, check out MacWorld's article.