I had a 135 Tele-Elmarit some years back, it was good optically but had some issues, including the googles were finnicky and needed adjustment twice. Mainly I like the M system for its compactness and the 135 Elmarit ran counter to that.
I do use a 135 on my M8 though, it's a Tele-Elmar of the first variety with 39mm filter and separate shade. I tried framing a few different ways, including over-rotating the lens past the lock so the 90 frames come into play, and an aftermarket zoom finder with 180mm on it. I happen to have an old Canon shoe-type 135 finder which has a very short eye relief, and when it butts up to my glasses, what is visible just happens to be almost exactly the right 180mm framing at infinity. Another nice thing about that particular model Tele-Elmar is the lens head unscrews and can be used on a Visoflex in conjunction with a short focusing mount. I've even mounted that to a 14167 Viso-to-R adapter, and that to an R-to-EOS adapter and used the Tele-Elmar successfully on Canon DSLR. Cool lens.
BTW I was watching "Without A Trace" on TV last night, and one of the FBI guys was doing surveillance photos from his car with an M8.2 and the 135 Tele-Elmarit. I wonder if that's standard FBI issue