17-50 EF-S and 16-35 EF is already the same length and weight. I was using the 17-50 EF-S fiter size of 77mmwhy does no one make say a 16-50mm f2.0 or something similar for crop cameras sure it would be expensive but i think people would be willing to pay for it, i would pay 70-200mm is f2.8 is money for it.The lens that you want is an excellent walk around lens. However, it may be a monster in size and weight. just look at the 17-50 f2.8 EF-S. It is 4.4 inches long, using 77 mm filter and weights 1.4 lbs. If it was f2.0 and 16- 50 mm, it might be using 90mm filter or larger and weighed over 2 lbs easily. The 16-35 already uses 83 mm filter. How many people will like to have a monster like tah tas a walk around lens and can be spotted from far away???
On a side not canon should make an L-s range for good crop for lenses like this. i aim fairly certain within a few years full frame will be less popular with the ridiculous iso performance of new crop cameras and the possibility of photo binning (don't ask me about it i'm a noob but basically you have option to reduce megapixels to get better iso performance)
Since he is rerferring to APS-C, I assume he means EF-s, which would be about the size and weight of a 16-35, but it would likely cost more.
as starting point and use the 18-55 EF-S (F3.5) 58mm filter size and the 16-35mm Filter size (77 mm) to guestimate the filter size. If between f3.5 and f2.8 (both EF_S) with increase of 19mm in filter size, I guest an increase of only 13 mm between f2.8 and f2.0 is very stingy. I have not yet taking the increase in viewing angle between 16mm and 17mm into account. With increase in the size of optical elements, the weight will increase also. It fact I may have already under estimate the size and weight of the 16- 50mm APS-C f2.0 lens.