while grab threshold is a must with rework of grab mechanics from solid line conection to ball axis with 360, 360, 360 on x y z. or Wii type of grabs
being unable to break grab is annoying as hell, and deformations of tori-body due solid line connection.
relax threshold is great idea aswell, tho it may be called pain threshold, so when you are hit quite hard your may loose control over your arm for a few frames as response to physical pain.
5-10 frames should be good enough, so toribash would not end up into stun-lock game, but have some neat feature that will make quality difference in gameplay.