135 F/1.8L IS USM <----- I Really wants one.
135 f/1.4L IS USM
That would put it in relative aperture size and MSRP to the 200 f/2.0L IS USM ....
There exists a Vivitar 135 F/1.5 from times past, and creates interesting imagery, but it's huge and not very light weight, something that the 135L has that is nice is it's good size, weight and sharpness. If the bokeh is great, creamy and without much CA then that's better than simply going shallower IMO (it can "feel" shallower too). It would be nice to shoot faster for those definite low light shoots, but ISO performance is getting better and better, so what compromises do we mind or don't for going for a faster 135L? It'll be cool though