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.
to use your argument of "solution to a non-existing problem".
Do you know you only need 40 hp in your car to drive 65 mph? So why a 300 hp or 400 hp or 500 hp Mustang? Why even a 150 hp Accord? Because people want it.
There is more to a price of item than "snob" factor. Zeiss knows how many lenses they can sell. Any good company with a half decent marketing dept knows how many widgets they can sell. So when you are armed with this information combined with cost of production, you can MSRP your widget.
As other posters have mentioned, there are videographers who could use this lens as well as photographers.
When you purchase Zeiss, you are also purchasing an extremely well engineered product combined with high quality materials. Nobody needs a handbuilt swiss watch. A $2watch does the same exact job. However, pick up a Rolex, Tag, Patek Philipe and you know you are holding something special.