I fully support this request. I work exclusively in jpeg, and wish to keep my photo collection storage to a minimum by overwriting the original when I am satisfied with the adjustments I have made.
(I have a complete backup of my originals should I ever need to go back to one - which is very rare).
I would suggest flashing a Warning such as "You are about to overwrite the original -- Is this what you want to do (Y/N) ?" and allow the overwriting...
Currently, I am using a workaround which is to "edit in" (e.g. Photoshop), select "edit original", edit the way I want, then save -- This will overwrite the original in LR. But I wish I could do that directly from the Develop Module.