A manual release system will never be suitable to stop the rapid pitch up caused in this situation. It happens too fast for a manual (actually a sensory-brain-muscle-manual) system, however good the manual system on the tug.

Glider CofG winch hooks are not really suitable for aero-towing, are they? Some of these gliders can't be controlled in pitch once the kiting starts. I have seen people leave their shoulder starts loose on areotowing, and that means the pilot can slide backwards - with hand held on the stick, so that moves too - on pitch-up. (Always use tight shoulder straps on launching, please).

I have lost two acquaintances, both gliding "greats" in such tug upsets. I would say banning the use of aero-towing using a CofG winch hook would be the safest bet to save lives, until an automatic system is available.I suspect this is something EASA and the FAA would sort very quickly ( the banning bit, not the automatic system). Sensors to measure pitch, rate rate of the tug, and also tug/rope angle and angular rate,suitably processed and actioned automatically could allow immediate release BEFORE the critical situation is reached - if we feel that we must continue to launch by aero-tow using CofG hooks.

A rule of nose hooks or "compromise" hooks only, meanwhile, would probably reduce the risk towards zero.