I'm sorry if any Zeiss fans find my opinion insulting, but to me this looks like yet another solution to a non-existing problem - at least as far as Canon cameras are concerned. I am not even going to consider the possibility that this would be a Tamron/Tokina "cheap" alternative - this is Zeiss, after all - so the only way to market this lens would be on the basis of quality.
Now, the Canon 70-200 f/2.8 IS II is good. Really, really good - so good in fact that a "better" lens would probably not produce any meaningful improvements for most users - so why should anyone want this lens - for the "snob" factor, yes, but what else?
Then there is the issue of IS and AF - sure, a MF lens like the 15mm one may be just fine, but for a zoom? This lens would need AF to be competitive - otherwise it would just be a way for people to show that have more money than common sense.