In case '[EPIC] Promote usage of "print->pdf" an article on mobile'[1]
isn't planned to be deployed sometime soon how about considering some
kind of temporary and helpful "quick fix"?
It could be something like filling the blank spaces of unloaded images
with some helpful text that act as links. The helpful text might be
something like, "Click here to see <unloaded> image", for example. The
user could be taken to taken to the location of the image file when he
taps the text. I'm suggesting this believing that it would be possible
to identify the unloaded images.
I guess this doesn't require much work and could be a "quick fix". This
is not required if [1] is being planned to be deployed "soon".
[1] : https://phabricator.wikimedia.org/T163472