Another source has come forward and said this lens is coming for Photokina.
“I can't say how I know, but rest assured Canon is replacing the 100-400 with a new version. It will have a better IS, be slightly faster at 100mm and have a zoom ring instead of the push/pull design. It will retail for $1700 US.”
I'd rather the push/pull, but I guess you can't weather seal that design.