The only "massively popular" lens that comes to mind is the long awaited and often rumoured 24-70/2.8L replacement. I guess the other lens, "a more specialised lens" could be the rumoured 35/1.4L replacement.
I'm just hoping the new 24-70L has an Image Stabiliser. If not, there's little reason for me to sell my existing stellar copy!
The 24-7- f/2.8L seems plausible, but I doubt Canon will include IS. One of the main uses of the lens is event photography (e.g. weddings) where the subjects are typically moving - which means keeping shutter speeds higher - depending on the situation mostly over 1/80s. That means that IS will not be a big benefit. I know my wife would not pay the price premium for an image stabilised lens at that focal length (assuming the price premium is similar to the premium on the 70-200mm lenses). The story is entirely different with a 70-200mm lens - to be sure to get a shot at 1/80s at 200mm, you need IS. That is why the 70-200mm f/2.8 USM IS II is so popular. I suspect that the market for 70-200mm lenses is probably much bigger than for 24-70mm lenses, which is why Canon can bring to market 4 L series variants.
In the 24-xxx focal length range, for image stabilised lenses, I would hazard a guess that Canon would get a better return on investment by upgrading the IS in the 24-105mm than by adding IS to the 24-70mm.