A 16-50 f/4 IS would be just the ticket.I like the idea of that, but would still love something really wide like the Sigma 12-24 II I used to own. I fear that Canon considers our dreams of a super wide covered by the 8-15 f/4. A lot of their articles have pitched it as a wide angle lens, but at least to me, I don't care for the fisheye distortion even if it can be minimized with a perfectly level shot.
seems to me there is market pressure for Canon to produce a rectilinear 14(ish)-24. its absense does seem conspicuous.
In addition, I don't see the 16-35 II going away or replaced. seems astonishing to me to suggest that, as the rumor has. Given its success in the market, and the fact that Canon appears to stick by it no matter what weaknesses the purests point out, suggests it is here to stay and probabably won't be updated any time soon. It would really surprise me if we saw a 16-35 III this year.
I see an 82mm mm 16-35 II, a 77mm 16-50 and a bulbous 14(ish)-24, all living happily together, as they would target different specialties. The extra FL, IS, and 77mm front end (I presume) of a 16-50 would be welcome advantages if f/2.8 isn't important , complementing the others, including the rumored 24-70 f/2.8 IS. THe 16-35 II is too succesful (strategically) to update it now.
BTW off the subject, but its kind of amusing to see the tricks that retailers go through to get around MAP and that is happening to the 16-35 right now. happens all the time I know, but its still amusing to think of the conversations among lawyers :-)