And very easy to do, I suspect it's on the todo list and they simply haven't had time yet. They can add overlay class to the tag and it should already work.
Yes I like the lightbox facility too. Any chance that images uploaded as opposed to linked could have thumbnails as in vb? Don't like the uploaded image details showing in the actual post.
When you click on the attached image's thumbnail, it just opens the full size image in a new page. With all of the pretty java on the site, it should also be implemented for the attachments.
6) Have a row of thumbnails for all available images underneath the current image.
7) How do you deal with images that are larger than the current viewport size? Scale them down in-browser?
8) Make it so we can use it easily in our add-ons. If you are setting your IDs and your JS relies on said IDs then it is hard for us to use it because IDs need to be unique. That leaves custom JS or pulling in say Highslide for our add-ons and bypassing your JS to avoid file edits.