There is so much complexity to what you're asking, that it's kind of meant to be as annoying as fixing the feets yourself.
Let me give you the reason why :
- First the origin of a character can be anywhere compared to the center of mass of the character itself. You could raytrace from the origin to the ground on the Y axis (hoping that you will not collide with anything weird in between), but there is a lot of chance that this might not actually by the "ground". You could try to make an average computation of all the nodes and the origin to find a better result, but this will still be somewhat not very accurate since a creator can completely shift the origin from the character itself.
- Removing the rotation from the feet could change the original pose depending on how the pose is made.
And this, is only a brief summary of what problems you could run into with a plugin like this.
Honestly, the amount of work required for this, is not worth the 3 minutes you spend fixing heels/feet positions. And even with the best motivation and intentions possible, I suspect it's quite impossible to get a proper result automatically. You
will end up having to fix/adjust the pose after the plugin pass... 99% sure.