New user here, but have been shooting both still and motion for over forty years.
Not a rumor, but some assumptions on my part...
Based on how Canon is promoting IS with tutorials and other marketing collateral presentations/literature on their site and elsewhere, I made the assumption that Canon is replacing most of the lenses is their most recent promotion with IS versions, supplemented in the lease case with the most recent optical coatings and manufacturing materials.
I own both the 16-35mm and 17-40mm. I typically use my F/4 lens series (17-40, 24-105, and 100-400 along with a 100mm f2.8 IS macro) when working in the field shooting wildlife, landscapes and for general backpacking. They are lighter and cut down on the load I lug about in the field. My f/2.8 lenses are almost exclusively used for in-studio and on-location product and advertising work. The latter is more because, I store the lenses in different cases best suited for different kinds of photography along with accessories I would generally use in those photography fields.
Increased ISO support aside, there are numerous reasons why a photographer would prefer to shoot with a faster lens depending on their current photo shooting session and these have nothing to do with ISO speed although increased or decreased ISO speeds do come into play in certain shooting scenarios.
Also an assumption on my part, but we may see some price drops as some older lenses such as the 70-200 f/2.8 IS Mark I are sold off, making it possible to drop the price of the Mark II (which appears to be happening already at some web sites). The L series TSE lenses have dropped a bit in price in recent weeks.
What I am hoping to see from Canon are some hybrid lenses better suited for shooting video with a DSLR. Canon manufactures almost as many interchangeable cine/video lenses as still lenses, so they have the technology. It would be nice to see a more modular high-end camera body that could be adapted to shoot both still and motion.
Increased zoom ranges would be appreciated in whatever ranges Canon decides to support. I've made some other assumptions about zoom ranges based on what the competition has to offer.
Would love to see the TSE 90mm upgraded to L along with macro capability. I sometimes use it with an extension tube for a lot of work I do both in the field and in the studio.
An 180mm IS Macro IS or a "L" zoom macro is on my personal wish list.
Regarding the 100-400mm, I use it by itself or with 1.4x and 2x teleconverters. This lens is unbelievably sharp with or without a teleconverter out to the edges. The panning IS mode is especially useful for shooting wildlife such as fast moving sea birds and other moving subjects. Unless Canon has some new mind boggling technology on the horizon, I don't see a replacement coming any time soon.
The zoom range of the 24-70 sucks. I hope to see it replaced with a f2.8 version of the 24-105mm f4 to allow some focal length overlap in the f/2.8 series of zooms.