[Brightcolours]

I don't think anyone does.

 

However, one has to remember that there is currently nothing remotely like a 24-70/2.8 on APS-C (or 28-50/2.8, for that matter). 

And it may replace not only a standard prime, but actually three primes: 18/1.8, 24/1.8, 35/1.8 (good look finding a 18/1.8  ).

 

I think the combination 18-35 + 85/1.8 could be quite useful. It comes close to the classic 28/2.8, 50/1.8, 135/2.8 setup, but adds a 35/2.8 and only uses two lenses (not sure that's an argument, due to the Sigma's size and weight, but well..).

 

Just out of curiosity, I am wondering how big this thing would have been if it were designed for mirrorless APS-C cameras. Should have been quite a bit shorter, shouldn't it? Equally "fat" though...

Well, it would still have to be a retro focus design (which camera has a flange distance of less than 18mm??)... So it probably would not be a whole lot shorter (see the 18-55 kit zooms on mirrorless lenses). 

 

Of course, I agree with you that some will find it very nice, especially in combination with that 85mm f1.8 (either Canon or Nikon). I even am sure that if someone were to give me that lens, I would enjoy using it.