Comment by michaelbuckbee

While the browser vendors haven't done this - some of the image hosting sites (who are far more directly affected) have.

Imgur automatically converts larger GIF files to "GIFV" (WebM or MP4). The size difference is nuts: their example is a 50MB gif being reduced to 3.5MB

Their announcement post about it: http://blog.imgur.com/2014/10/09/introducing-gifv/