I like the idea in general. However, this would mean quite some changes to the current behavior of browsers and some impact on the user experience:
- Double downloads due to the source and the canonical source being different files, leading to increased traffic
- Users cannot easily download the exact image they’re viewing currently. This could lead to files being downloaded unintentionally (it could be any file that is linked as canonical, even an .exe/.dmg). Also, if a user wants to get the webp file this is not easy to achieve anymore with this change.
Just some considerations to make regarding the user experience and security impacts. But maybe there’s a nice solution to tackle these concerns.