Go Sigma! This will have to a pretty fabulous lens, though, as the 135L is easily my favorite current lens from an IQ perspective. Still, the thought of having a good stabilizer in a lens like that would be huge.
I'd love to see a great 50mm f/1.4 from them, too. I'm not even using a modern 50mm right now, as it isn't a huge need for me. I use either a 55mm f/1.8 SMC Takumar M42 lens or a Helios 58mm f/2 lens when I am shooting portraits/narrow DOF shots in that range and just use my Tamron 24-70 VC for most times. Every current 50mm lens for a Canon mount has one quirk or another.
Exciting times. I really, really love that Sigma and Tamron are actually producing some lenses that are pushing Canon and Nikon right now. That will help all of us.