I wished we had something like this long ago. I hate developing CSS and DOM scripting for IE6 separately from newer browsers. It always goes something like, "OK, all done! Oh, crap, I wonder what it looks like in IE 6..."
Please join me in backing this movement. I hope this movement continues for when other browser versions become obsolete. Clearly I wouldn't suggest this for my clients' sites, per se, but I don't mind adding this to my own personal sites in order to raise awareness of what happens when people wait too long to upgrade their browsers.