Just for your reference, based on:

http://www.sitepoint.com/browser-trends-november-2013-ongoing-ie-increases/

Global IE8 and below marketshare would probably be ~10%, which is not insignificant.

As for downgrade solutions, it really depends what you would have happen for users below a certain threshold -- should we point them to a different browser? I could find a js way to do it probably without every that might be more verbose but work on lesser versions of browsers, but its all a matter of time/prioirties.

Also, do we know our support in general for the ~98% browser use case? As in, I've been using data attributes and HTML5/CSS3 stuff, and my JS has been mostly using "newer" things. Do we have a process to test on the top X browsers (I test on Chrome/Safari/Firefox for Mac, but not Windows versions, IE, Opera, etc)