Yes, I could see a 35-135mm f/2.8 as being a very useful lens for some situations (eg street photography, candids at camps, events, etc)
There is the Tokina AF 50-135mm f/2.8 AT-X Pro DX - some reviews of it in different mounts at photozone.de - and it does well, particularly at the wide end across the frame, and tele end centre is great, just a bit soft in the corners wide open. But just 1 stop down the corners improve substantially.
There are also 3 versions of the Sigma 50-150mm, two of which are tested at SLRgear.com (they vII they appeared to have a very decentred copy). But the vI Sigma 50-150mm ƒ/2.8 EX DC OS HSM APO they tested is amazingly sharp across the frame at all focal lengths, even wide open.
To me I know I would find a 35-150mm f/2.8 image stabilised lens 'ideal' for many of my purposes - that is, that focal length on an APS-C (Canon 7D). For FF I'd want to use a 70-200mm f/2.8 though.
Here's hoping!!! I have a 70-300mm L - which is what I use for my wildlife / bird photography (as I don't need fast glass for that)... and my walkaround is my Canon 15-85mm. A moderate fast (that is f/2.
35-150mm would be great for people photography or subject isolation.... so yes, it would also fill a niche for me.
At times I use my Canon 100mm f/2.8 USM macro for subject isolation (ie - not macro) - which does well in that too- but just at 100mm obviously!