It will be a long time before this catches on for the web. The web will be the last place to adopt this.
The first step is for Adobe to adopt the format. It has started to in some products, but is not in the current version of Photoshop. Is it in Photoshop CS6 does anyone know?
Once this happens, I think it will catch on quickly with photographers. For storing images at high quality (>8bit per pixel mainly, also good compression options).