I have to say, I never understood the need for a gif-like animation in a png-like format. Gifs have incredibly basic animation that's difficult to control in most (all?) browsers, and it's pretty useless for everything except brief clips on tumblr.

Here's your animated png format, put all frames of the animation in a png sprite sheet, and fill early pixels with metadata. Add in a small library and you've got a format that's allows for more advanced animation than gifs, with the better compression and alpha of pngs, and is supported right now in any browser with decent canvas support.