sorry to necropost, I've just had a very similar idea and this one seems like a particularly good suggestion now that pulping's back and I'd like to expand on it a bit.
So, "curb stomping" is an effect (a change to the collision formulas) to be applied when the attacked bodypart is pressed between the attacking bodypart/object and solid ground/wall/treetrunk/minecart and is unable to be moved out of the way. It is meant to increase the attack's force and lethality, because no energy will be transferred into the motion of the target and thus more of it will go into deformation of both the target and the percussor (though the latter isn't implemented yet).
Instead of introducing new attacks though, stomping effects should activate (in a percentage of cases perhaps) whenever an attack is directed against a bodypart that can feasibly have contact with the ground or wall atm. So, let's take a look at a few examples.
upright Human A is using his left foot to kick the right foot of the upright Human B. Since right foot is a [STANCE] bodypart, it has a fair chance of having contact with the ground, so this attack should be treated as a stomping attack with a decent probability (around 70% probably, the rest amounting to the kicks at a lifted foot and kicks to the side of the foot).
Standing goblin G is swinging his mace at a prone dwarven child C, aiming for the head. Since C is prone, any bodypart has a good chance of having contact with the ground, so this attack should have a good (0.8 or more)probability of been amplified by using a stomping calculation against a usual collision calculation.
An adventurer A standing hiding next to a tree trunk is being shot from behind by an elven archer. Since A is hiding and thus likely tries to position himself close to obstacles, any bodypart should be assumed to have a decent chance of having contact with the tree, thus making it feasible to use the stomping formula to calculate the attack. Moreover, a separate penetration calculation could be made here to determine if the target bodypart should be nailed to the tree by the arrow.
To make it more lively and veritable, some additional mechanisms may be wrapped around it (for example, if you detect an incoming attack aimed at your foot and you don'd want it to be stomped, you can use it for kicking and thus avoid the stomping effect)
The implied connection with pulping here is that regular attack against a freehanging or raised limb shouldn't have that big a chance or potential to cause pulping damage, because a good part of the energy would've been transferred into kinetic energy of the target. Target being pressed against the ground or walls is where the most extensive damage (leading to pulping and bisection) should occur