(T48936 comment 2)
However what we could do is never serve the original as a thumbnail.
The original is always available if a user visits the "File"
description page and downloads it, but when an article embeds an image
at a size that happens to not have a smaller thumbnail size available,
we currently serve the original. We could probably change that to even
serve a thumbnail for the nominal size (like we do with SVGs), which
would presumably make our urls a lot more consistent and allows for
better optimisation of smaller images.