I'm not sure, but I think you're also suggesting that image load times would be faster if this was implemented. They wouldn't - you would have to wait just as long when you hover over the image for it to load as you normally would.

This might improve page load times over all if people were posting lots of large images all the time, but it's not really that common. Same principle as the Youtube Fancybox suggestion from a while back. Every little script and customization added slows the site down just a little bit more, which is why I'm trying not to add too many.

The nice thing about forums is that they're not a tiny, limited comment section on some article - the comments themselves are the focus of forums. We don't need to eliminate any formatting from them.