This would be a nice addition, however, old replays, styles of fighting, etc, would be greatly impacted by this change. Also, if I'm not mistaken, different mods have things/things similar to this.
On the other hand
Making this sort of a default setup, or using the normal tori figure and making a well working script or something for say, could prove to be indigenous to the game.
Overall, I'm meh about it. Things like this should stick to mods.
People really need to give up with changing the default Tori... it would have such a large impact that it is never going to happen PLUS this can be done in the mod maker if there is such a large demand.
Try relaxing your lumbar? I heard that relaxed joints move faster, so maybe once you've got the movement going with enough speed and momentum, maybe you could relax the lumbar and let physics do the work.