Editing clipping paths is now a toggle. If you enable it, editing
controls will be displayed for clipping paths, in addition to normal
editing controls.
I did not test the branch, but I just wanted to point out that there already is a toggle in the node tool toolbar that
displays the mask nodes (available in 0.47). But maybe I didn't understand what your code is doing.
Using the right-click menu doesn't suffer from this, because it
doesn't introduce any new concepts - it is just a shortcut that
combines creating a rectangle of the same size as the image and
applying it as a clipping path. It would behave in every respect like
a normal clipping path after that.
Then we could extend this functionnality to any object. It could be placed in the Object>Mask menu and in the right click menu. It could be called "Create Mask from Bounding box"
What do you think ?