My bet is, much like the aforementioned 70-200 2.8, the improvements will not show up on paper, but in performance.
To do otherwise wouldn't be an upgrade. It would be a new tier of lens.
My prediction for what little it's worth: 100-400 or close to that, non-push-pull, better optics, better IS.
And I'll throw in with the heretic and say for fast zooming, I like the push-pull. However for general use, I do prefer the twist ring.