Maybe this means that a Sigma spy within Canon has gleaned that they won't be adding IS to the 135L anytime soon.
If it's as good as their Art 35 and the AF is close to the 135L then I'd certainly consider it.
Canon's probably already scrambling to get a 35L II out the door to catch up with Sigma... An Art 135 OS and 50mm would really hit Canon where it hurts.
The Canon ef primes have been a nice earner for Canon. Many wedding photographers have stayed in the Canon fold (when Nikon had better DSLR specs) becuase of the 35L, 85L and 135L. No other band (other than Sony) had a simular array of bright primes. But as usual Canon were unaware of the need to develop the next gen of fast primes. The 35L is a fantastic lens, but flare control isn't great, it's AF in low light is erratic and it's not weather sealed and it's number of aperture blades is an even number. The 135L is an awsome lens, but it's an old design, flare could be better, MFD could be better. It could do with newer coatings, it's aperture blades are not circular (stop down and look at the out of focus blobs). It's not weather sealed and Sony has an f1.8 variant, which means that it's not the best of the breed. Popping IS on it would really make my wedding work easier too. It's AF is good but not as good as the newer 70-200 f2.8 L IS II. It#s a great lens but there's quite a lot of room for improvement.
The 85L is a quirky lens and I'm quite happy with it as it is. It's not easy to use, and it's dof is so slim it requires a well honed AF technique to get consistent results. I use this lens a lot and I love it.