I don't own a 135 f/2 at the moment but it's a brilliant piece of glass which feels very last century now that I've been spoiled by IS in the brilliant 70-200 f/2.8ISII. My 135 f/2 wasn't getting any use so was traded. I don't hold as steady as some photographers who can hand-hold at insanely low shutter speeds. I do value IS! The 135 f/2 lens would be a popular candidate for upgrade. I'd like to see it presented at the design level of the L100 f/2.8is macro. Even with the inevitable price boost, this would be a great seller.
EF50 f/1.4 would be another welcome upgrade, as would an optically improved 16-35 f/2.8III. Lessons learned in the redesign of the 24-70 f/2.8II may flow through to the 16-35.
There will always be time lapses in the development cycles, but that's life. But overall I see Canon's lens set as offering brilliant choices for just about any shooting style or special project.