Way too much stuff needs it. For example fun little browser games. For example http://www.kongregate.com/ http://www.miniclip.com/ http://www.friv.com/
At least in my browser (Firefox on Linux) flash plays better than html5 for video.
We already have a way to transmit two-way video live in browsers (WebRTC).
It should be not to hard to use the codecs existing for that to make a one-way live streaming in browsers.
If someone would add a small standard extension (like Microsoft originally suggested) to allow for one-way streams, we could do livestreaming over it, too.
Preferably even make it seamless – allow pointing a video element to a livestream source.