I don't see what I'm not understanding. I'm not talking about attachments. The image proxy is used to avoid mixed content warnings on hotlinked images, it is not used with attached files, as it is not needed. It sounds like your images broke on that other site because they ran some sort of...
It's because a page which loads non-HTTPS images will show a "mixed content" warning saying that the page isn't secure, even if the site is HTTPS. Here, we have an image proxy, which proxies the images through our server before loading them, to avoid mixed content warnings, without breaking any...
I can edit posts which were made a few days ago under this account. I don't think we changed the post edit times with the upgrade.
We already redirect non-secure HTTP links which go to pages on this site to secure HTTPS links.. I don't see how that could cause any problems, as long as HTTPS...
It's still pretty similar to how it was before, but there are some fun new features, like additional post reactions if you hover over the like button.
It also supports all the unicode emojis, and it has a much better text editor.