I have no desire to trade a large aperture for is. I used to consider only lenses with is... but I shoot at apertures and shutter speeds that don't require Is. And with usable isos of full frame... I have to be in near pitch black... ok that's an exaggeration, but still.
I can certainly understand this as I have a host of large aperture lenses.
But, I think the new Canon "IS" line of primes - including these new ones - are probably the most practical solution for 99% of photographers out there. And in some cases, they have some nice improvements over what they are replacing not even including IS. They aren't necessarily the cheapest, but they offer a great combination of features, build, and image quality.
First, two of the lenses most notable for being able to "shoot in the dark" are the 50mm f/1.2 (my current favorite lens) and the 85mm f/1.2. However, by having an aperture this large you can run into focus shift issues, lesser performance when smallest aperture is desired, slower autofocus due to more glass to move, and potentially increased lens flare at smaller apertures. The IS alternatives that will be at f/1.8 might not get the magical bokeh of f/1.2 nor color/contrast on par, but it will be somewhat close and still have excellent dark capabilities at f/1.8 - enhanced even moreso by IS. The f/1.8 IS lenses will autofocus faster, be lighter, usable in all scenarios, and require less skill to use. Thus, for most photographers they would probably be a better buy at least for general usage. For specialty usage, the 50 1.2/80 1.2 will remain supreme... But that does not mean these lenses are junk, I would just say more practical.
The 135mm f/2L is an interesting case because it does focus quite quickly and is easy to master - plus it is comparatively cheap. However, it also is an older design with straight aperture blades that can result in angular bokeh balls that can be distracting - and the focal length is getting a bit long without IS indoors even for f/2. When shooting dimly lit indoors, I generally like to keep things at minimum 1/100 to get sharp pictures in avoiding motion blur while still letting a decent amount of light in. But at 135mm, 1/100 introduces increased risk of camera shake - thus I'd have to increase shutter and perhaps ISO to keep things where I'd like them. For these reasons, an F/2L IS 135mm would be much welcomed. While this rumored 135mm is only f/2.8, pricing suggests that the F/2L will likely be discontinued and probably replaced by an aforementioned F/2L IS, and the f/2.8 IS will fill the under $1000 price vacuum created as a result. And it will have curved aperture blades for nice circular bokeh balls!
So, while I also would often not trade larger aperture (f/1.2-f/1.4) for smaller aperture ( f/1.8-f/2.8 ) + IS, it is rare that the former offers no disadvantages and the latter no advantages. In fact, I'd say for most the new "IS" range is probably the best bang-per-buck combination in the primes. Another example at 24mm - the 24mm f/1.4L II lets in tons of light, but for the typical usage of 24mm landscape, the 24mm f/1.4 is much more flare-prone at f/8+ than the cheaper 24mm f/2.8 IS; at 24mm I'd actually prefer the 2.8 IS over the 1.4L. With Canon zoom lenses, though, getting the more expensive L range is almost a necessity as the non-L lenses are too slow (f/4+).