Is the BBC not able to work pngout, or zopfli into their workflow? I wonder, because using pngout on your image saves 3%, and zopfli saves 6% both losslessly. They are missing out on a 50KB savings , simply because they can't run a command line program? Here is a losslessly compressed version of your banner http://i.imgur.com/NUhAsrA.png I made it completely automatically.
I should also point out that I no longer work for R&B Creative who are responsible for the BBCWW websites, so I won't actually be doing anything
As for other features see http://www.libjpeg-turbo.org/About/Jpeg-9. In short.. they are non-standard extensions and rejected by ITU-T.
WebP already has the same issue, it's not fully backwards compatible and some features are optional.Even so, when you use jpeg with arithmetic you never know if the user will be able to see it or not - which makes this really useless.