Who would buy a 135 / 2.8 IS?

Great Bustard wrote:

Canon has released some really nice lenses as of late in the form of the 24 / 2.8 IS, 28 / 2.8 IS, and 35 / 2 IS, the latter being, from what I can tell, the most popular. One can only hope that Canon will continue these updates by making a 20 / 2.8 IS, 50 / 1.4 IS (the 50 / 1.8 update is rumored to be an STM lens without IS), 85 / 1.8 IS, and 100 / 2 IS.

But would anyone have any interest in a 135 / 2.8 IS? I mean, it's a stop slower than the fantastic 135 / 2L and the same speed as a 70-200 / 2.8L IS II. So why a 135 / 2.8 IS? Well, it would be quite a bit smaller and lighter than the 135 / 2L (think 35 / 2 IS vs 35 / 1.4L) and have IS, but would likely cost about the same. I think for many, the differences in size and weight, along with IS, would matter more than the extra stop. For those that it wouldn't, Canon would still have the 135 / 2L (or Sigma, possibly, a 135 / 1.8A OS).

With regards to the 70-200 / 2.8L IS II, well, it would be way, way, way smaller, lighter, and less expensive. One could argue that a trio consisting of an 85 / 1.8 IS, 135 / 2.8 IS, and 200 / 2.8L IS (if Canon ever made such a lens) would be comparable in price to a 70-200 / 2.8L IS II, but be significantly smaller and lighter when mounted on the camera.

So, with that in mind, would anyone get a 135 / 2.8 IS at about the same price as a 135 / 2L?

Your points are totally valid but from a manufacturer's point of view such a lens is not likely to be a priority at the moment because the potential sales would be quite small. At one point in history 135mm was probably the most popular focal length after 50mm. But once reasonable quality zooms in the 70-210 range hit the market interest in 135mm lenses declined markedly. For enthusiasts who needed a fast 135mm with apertures such as f/2.0 there was still some demand but it was not large. For everyone else the zoom was much more versatile, even if heavier or slower.

I suppose the question is once the manufacturers no longer have the soccer moms as a market and the market really starts to shift back to enthusiasts / pros in earnest, will those enthusiasts' demands include the desire for a 135/2.8 in sufficient quantities for it to be worth making one. Technically it's not a problem.