My idea uses a similar set-up to the rapid changer for locking, however doesn't use a constant taper. It uses a small taper to maximise locking force at the locking point, but to avoid needing an excessively long taper, the taper changes into a recess to allow the ball to drop away for release clearance.
Then to avoid needing as much force to ensure a good release, you have a set of balls above the pull stud that are pushed by one moving taper, into another stationary taper to force the holder down.

The tapers are designed such that the release taper doesn't contact the release balls until the locking ball taper has moved away from the balls. Sketches show it would need a taller pull stud than normal to allow room for the two tapers. I'll tidy up my sketches later and scan them in. I'd put them in CAD, but I'll probably not use that option, and I still need to build a router!

Personally, I think a scaled down INT/CAT/BT ATC would be a better option. Mount it to the side of whatever motor you have, and drive it by a belt/gears. It would increase weight a good bit, but you'd have a tried and tested system, with lots of clamping force, and less balancing problems.