Why not produce a 50L which is the 50 many photographers wanted as a robust, high quality L lens which is a razor sharp f1.4, and keep the current 50L as a specialist 'art' or portrait lens.
It's annoying that those of us who like the 'standard' 50/1.4 have to put up with such a flimsy, cheap plastic lens, with appalling manual focus, no full USM, WS etc.
Where would this leave the rumoured 50/2 or 50/1.8 IS ? Well maybe that lens is going to replace the current 50/1.8 as the cheapest prime that is very popular as a first lens to compliment the kit zoom.
The topic of whether the new non-L 50 IS will be the base-level or the mid-level has been heavily speculated already in these forums.
Personally, I think it will be mid-grade and replace the 50 F/1.4 (old-)USM. I just can't see the nifty fifty being retired -- it holds a unique price point and serves a common need as a photographer's first prime.But
there are those that would correctly argue that all of the non-L IS USM refreshes to date (24/28/35) have replaced the cheapest non-USM
lenses so far.
Whatever line it replaces, that new lens will sell like hotcakes. It will be sharper than the 50L (heck the 20 year old 50 F/1.4 is already sharper today at some apertures), lighter, have IS, have true internal focusing (without the front element sliding inside the housing), and have proper modern USM. The only thing it won't have is weather-sealing and the widest possible aperture. But even at F/2, I'm probably buying that lens.