I thought so too. But your test example is 2MB and the one in Fantasmos' problem thread is 4MB... I tend to back out of map threads when I discover someone has embedded 15 feedback screenshots that are each 1.3 MB because it is annoying. I fear it might get worse if Fantasmos and others are using them for stuff that is STILL huge for an embedded image after being webm'd.
Did a hacky hack to get non-preload to work - hopefully it doesn't break on too many gfycats.