Wow.
My gut reaction to this is pretty negative. We would be adding "Stuff That Coders Like", that will confuse everyone else, make shortcode insertion very prone to errors, make newbie site owners freak out, and probably break lots of stuff out there.

When I need shortcodes to do fancy or odd stuff, I can code for that behind the scenes. I don't want to subject normal humans to it. We don't allow PHP in normal editing spots. It would seem that this is moving in that direction. And as you can see above, readability takes a big hit - it could end up nearly as "fun" as regular expressions. :)

btw, great point on characters missing in non-English languages. I hope people continue to keep those in mind.

I am pleased that they're taking a pause for the cause on this.

Dave