I would really like to be able to have more control over how the transform constraints link different bones together.
I find myself doing a lot of perspective looking motions where I want the scale of a bone to grow in relation to the translation motion. For example having an animation simulating moving towards an object that then passes by the camera/screen.
For that purpose it would make sense to be able to link the scale values of a bone to its position values in x or y or both. It would also need to be able to consider some form of offset to this value so it would be possible to have the scale value be (x_position*2) or (y_position+1) for instance.
So what I'm proposing would be a version of the transform constraint that has a small script/formula input that can take simple arithmetic combined with bones attributes either on the same bone or another target bone.