It got me wondering if running a stiff outer spring would allow for keeping the "shock absorption" feature when applying the rear clutch, while also providing some mechanical assistance with the line pressure to reduce the time for the piston to top out into the case when the front servo is applied. Or, maybe some combination of outer spring and reduced -- not completely blocked -- piston travel.
You're thinking correctly; the stiffer the outer spring, the more cushioning for the rear clutch apply and the presence of the spring
does help make a quicker (firmer) shift. The factory used a variety of outer springs, some so weak that even a geriatric like me can compress one to coil bind with two fingers.
Reduced piston travel would mitigate the cushioning effect so it would be counterproductive.
