I think it is a fair statement that Canon´s 50mm line up is getting a bit old. I have used the 50/1.2L for many years and I have been very happy with it. It adds a creamy and artistic dimension to images you don´t easily get from others.
But! It is quite clear that they need to upgrade these lenses to match what the competition is bringing out. The Otus is totally crushing every one of them, but at a very high price premium. The 50 Art is cheaper and even though it will not be as good as the Otus, it will still outperform every Canon lens by a significant margin. I have not seen enough to say that it will contest the bokeh of the 50/1.2L, but the 50/1.2L cannot contest the other qualities of the Sigma or Otus. It´s a bit like saying that a 16bit CD concept outperforms a 24 bit SACD concept (analogue part excluded). It does not.
I also believe that the 50 Art gave both Nikon and Canon something to chew on. They may well have planned the release of something a bit better than they have provided and probably add IS. But with the 50 Art out, they have to go back to the drawing board or alternatively risk losing the 50mm segment to someone else.
1DXII, 5DIV, 5DSR, 8-15/4L, 11-24/4L, 16-35/2.8L III, 24-70/28L II, 70-200/2.8L IS II, 100-400/4.5-5.6L IS II, 200-400/4L IS 1.4x, 17/3.5L TS-E, 24/4L TS-E, 35/1.4L II, 100/2.8L IS Macro, 300/2.8L IS II, 600/4L IS II, Zeiss: 15/2.8, 35/1.4, 55/1.4 Otus, 85/1.4 Otus, Profoto B1