The grey market price is not much more than the Sigma, looks like an easy choice if one is buying it new:
€669.00 - 12 Months Warranty - 14 Days Money Back
www.e-infin.com
If they can make a lens this good already for SLRs, how much better it could be without the restrictions of the longer flange distance.
As far as where Canon and Sigma is heading, it seems though that for a mirrorless mount, they would rather just make it even faster.
Which means doing a
35mm f/1.2 and raising the price further, rather than reducing the size and weight (making it more proportional to the camera bodies) and keeping it at f/1.4.