Love my 100-400, would appreciate better IS, full sealing, and optical improvements. If it's as sharp as the 70-300L, awesome. Hope they keep push-pull, but could learn to live with rotating extension.
Expensive, yes it will be. But probably worth it.
100-400 F4 without 1.4 extender, Would be a good alternative to the 200-400 maybe half the cost?
Ha ha ha. 100-400mm f/4 means the same front element size as the 200/2, 400/4, 200-400/4, etc. Would be a $7K lens easy. Get off this, folks, it'll be f/5.6 at the long end, and likely close to $3K at that.