Who will be buying this?
I'm definitely interested. Waiting for reviews first, but I like the size/weight/flexibility for travel, walkaround, and it would probably be close to ideal as a single lens solution for my backpacking trips, too. The buying decision for me will depend mostly on the optics.
I do find this lens way more interesting than the 24-105mm f/4 IS; it should hopefully offer better IQ, smaller size/less weight, and the macro mode is appealing as well. So (potentially) the only significant trade-offs are aperture and less zoom range than some might prefer (although personally I'd rather have a smaller zoom range and better optical performance).