I was thinking of it sort of as a feature that we don't kick off an image load right away on mouseover, since it could affect performance (including during scrolling, which has always been so sensitive).  If the image is going to take an annoying length of time to load, the extra ~1/3 sec might not be noticeable anyway.

But your 2nd suggestion is the ideal in my mind.  I held off on doing that originally because I was worried it'd make the pull request too disruptive... but happy to do it now.