But presumably it would still work with 3rd-party extenders?If the 100-400 is as good as Canon's recent new offerings, then it should be markedly better than the 70-200L II + 2x III. Hopefully, it'll take extenders well and give us good IQ at 560mm, which is about as far as we can get with a mobile hand-holdable system.Hopefully, it'll take them at all. Lots of people are clamoring for a rotating zoom like the 70-300L. What if that plus a compact design means the lens loses extender compatibility?? Why would they do that? Consider...all along the 'barrier' was 400/420mm. If you wanted longer and still wanted AF, you shelled out the big bucks for a 1-series body or a supertele. So now that they've put f/8 AF in a 5-series, perhaps they'll take away a 'cheap' 560mm f/8 IS option with good IQ. Not really trying to be the voice of doom, here, but we all know that Canon giveth and Canon taketh away (AFMA on the 60D, anyone?).