The reason this (faster ramps, accel/velo for the same or even shorter events to conserve cranking pressure and duty cycle) is not more commonly used is that it:
1. requires a harder, finer finish on parts, especially those with scrubbing contact (lobe/tappet, stem/rocker)
2. requires higher spring tension for the same RPM
3. requires stiffer pushrods (anticipating pushrod as the weakest link, in some cases it will be the rocker)
4. reduces service life
