I bought the 50 Art last year, but still have to do my first fashionshoots with it starting this spring in combination with 85 & 135mm.
Yes I can use the 70-200 2.8LII but less heavy faster primes with nice DOF/bokeh are always a pleasure to use.
Before I had the 35 1.4 Art, but I tended to put too much background in the picture.
As I have to focus more on the model + the clothes for fashion, the 50 1.4 seemed perfect.
Any modelshooters over here that use it much or are you all 70-200, 85, 135, 200mm portraitfreaks ?