The last time we were told about a new 135mm lens, it turned out to be a new lens, the TS-E 135mm f/4L Macro, which will have its fans in a niche market. The 135mm lens a majority of people were looking for was an update to the classic EF 135mm f/2L USM.
The EF 135mm f/2L USM was announced in April of 1996, so it's likely we're finally going to see a replacement and the addition of IS seems to be a logical next step.
We're told that a new and fast 135mm is planned for next year and that it will have IS. We're wondering if a bunch of IS fast primes have been designed alongside the recently announced EF 85mm f/1.4L IS USM, as we heard recently that a new 50mm f/1.4L IS is also out there in prototype form.
We get the feeling such a lens will come deep into 2018, and it won't be something we'll see for CP+ in February.
This is a [CR1] rumor, so please treat it accordingly.