With a lens like that, I could see a lot of happy owners of the current 50 f/1.4 being prepared to buy a new lens.
I've already got the EF 50/1.8, Takumars 50/1.4 & 55/1.8 & 55/2.0, FL 55/1.2, Zeiss 50/4.0 (x3), OM 50/3.5 macro, and just recently a Schneider Retina 50/2.8 (in the post).
And with all of them, even I
'd be interested in an EF 50/1.4 IS. You can never have too many fifties...