I've just been doing my first rig that has lots of bones constraint by the same transform constraint, and found something I hadn't realized: the order in which you select the bones to be constrained matters (makes sense now that I think about it, for the same reason order of constraints matters).
However I was disappointed to find that you only seem to be able to change this order by starting from scratch and re-selecting each constrained bone in the order you want. Since Spine already has the nice pop-up vertical list of constrained bones when you click on the abbreviated horizontal list, why not just let users drag to reorder in that menu?
This would be somewhat similar to how you can change the draw order of bones that are bound to a mesh.
Also one more improvement for selecting which bones are constrained: after clicking the little 'pencil' 'edit' icon to initiate choosing bones, holding shift could add new bones instead of starting from an empty list. Or instead you could hold shift as you click the 'pencil' 'edit' icon.