- works inside an <img> tag
- works in background: url()
- supports both smil animation and css animation
- supported back to IE10 (with css animations)
- plays automatically in a loop with no play controls
- can embed jpegs, pngs, videos as videostrips or diff images
- can apply alpha transparency via a mask operation
- flexible enough to apply a wide variety of compression techniques including multiple update regions (where gif only supports one rect per frame)
- Controllable via javascript (as long as you trade off putting it in an img tag and use an object tag instead)
previous comments here: https://news.ycombinator.com/item?id=8038838
all that's missing is widely available software to author SVG animations.