One possible risk with MediaViewer is that providing an image information page with no edit functionality might reduce the number of readers turning into editors, or the number of editors who were not active in the file namespace starting to do so. This was especially a concern on Commons (although it is less relevant now that MediaViewer had been disabled by default for logged-in Commons users). This should be measurable by counting edits made by users with low editcount pre- and post-deployment. It seems that Edit already collects the data needed for that.