The push-pull is probably the feature (other than focal length range) I like most about the existing version. So expect it to go to a slower less accurate modern twist design for the next version. Radical thought: is there any way they could come up with a reliable physical design that allows both twist and push-pull zoom on the same lens?
I don't have any major complaints of the existing version. About the only problem I have is water ingress and I've dried it out on more than one occasion, so better sealing on a new version would be a big plus for me. The other is that a shorter minimum focus distance would be really nice, and faster focus speed.
Canon 1D, 300D IR, 450D full spectrum, 600D, 5D2, 7D, 7D2, EF 35/2, 85/1.8, 135/2+SF, 70-300L, 100-400L
EF-S 10-18, 15-85, MP-E 65, Zeiss 50/2 macro, Sigma 50A, 150 macro, 120-300/2.8 OS, Samyang 8mm fisheye