Yes, better support for display of images through a modal viewer would
be great. I'm not sure a "modal" parameter that has to be explicitly
set for files is the best approach - I would recommend optimizing the
default experience when a user clicks an image or video. It's not
clear that the current behavior based on a pixel threshold is actually
desirable as the default behavior. (On a side note, the TMH behavior
should be improved to actually play the video immediately, not require
a second click to play in modal view.)
Magnus Manske explored an alternative approach pretty extensively in
response to the October 2011 Coding Challenge, which is worth taking a
look at:
https://www.mediawiki.org/wiki/User:Magnus_Manske/wikipic
Cheers,
Erik