This idea fixes a small ux issue, but when you load a discourse forum with a cold cache, there is a small moment when you can see the image loading (depending upon your hosting setup, it can take longer or shorter amounts of time). It would be nice if Discourse preloaded both header images in the background, so by the time a user scrolls, they don’t see the loading part.
You can see it on meta if you clear the cache, but your CDN loads so fast it isn’t very noticable. On my hosted copy, it takes longer to load and is thus more noticeable.
Other images that are easy to see being used on the site should probably also be preloaded, but I’m not sure how you would find those. Most of them, I’d imagine, are probably used right away anyways.