So. Am I to infer that if Canon comes out with 50/1.2 II that is sharper and has better corner to corner sharpness then you would not DESIRE to use it?
It depends entirely on who "you" is and what s/he wants to do with it. If you like that dreamy look, and if you use the lens to take portraits (in which case the chances that anything in a corner would be in focus anyway seem slight, rendering - pun half intended - corner sharpness moot), you may not want such an improved lens at all.
And if you do want better sharpness, including sharp corners, why not get the new Sigma - or do something different altogether and buy, say, a Sony A7r + FE 55 1.8? Do your lenses all have to have "Canon" written on them?" Your complaint looks rather like another manifestation of the fanboy-ism that keeps getting brought up: Does Canon have to make the best of everything according to some notion of "best" that may or may not be widely shared?
(And leaving all that aside, for now if you want a 50 1.2 (or 85 1.2) lens for a ff camera, regardless of brand, are there better alternatives which are also 1.2? There are new similar lenses from Fuji and Panasonic/Leica, both supposedly marvelous, but they're APS-C and M43 respectively, but that's not quite the same thing....)