How many would choose stellar 50mm f/2 IS over a mediocre 50mm f/1.4/1.2?

agreed. it's all matter of personal preferences.

as for focal lenses I myself consider "nice" (it doesn't really need to be exciting - just usable is perfectly enough) - 24mm with both FF and crop, 35~38mm FF, 135mm crop.

it's the 135mm I miss the most in Canon lineup. I'd love a decent 135/3.5 IS for a pricetag aroung 700 EUR (after the dust settles) and weight/size like the old 135/2.8...

50mm... I've Sigma 50/1.4 which is nice, but the focal length is neither wide enough to me in FF, nor long enough in crop