All of the browser vendors are supportive, all had initial prototypes etc. Speculation: The spec is still a Working Draft aka: comments welcome from anyone, ma

All of the browser vendors are supportive, all had initial prototypes etc. Speculation: The spec is still a Working Draft aka: comments welcome from anyone, may drastically change. Chrome already intends to ship soon. It's quite possible that Chrome is rushing ahead as usual even though the spec hasn't been fully finalized.