Hi RGF, there's a similar thread running "200-400 Predictions" so you may want to check that out. Copy of my comment on that thread.
"I was invited to a Canon/Cathay Photo Preview Session in Singapore in January this year (2013) purely about the 200-400f/4 (1.4x), We were able to play with production Lenses (According to the Canon People there these were Production Lenses), we could use our own cameras, but no Cards, on both my 1Dx & 5DMK3 Bodies this lens feels & looks the part, until we get to view Images we wont know for sure, but I feel it's at least as sharp as my 400f/2.8 V2 Lens, time will tell. Weight wise a fraction less than the 400f/2.8, maybe a few mm's shorter, it's not a small Lens, hand holdable if your reasonably adapt at holding the 400 V2.
Pre orders were taken at the Viewing by Cathay Photo, and an "estimated" delivery time was given of "Before June 2013", Since then I've heard nothing to detract from that statement, other than I have read a report that the Lens has been delayed due to "redesign requirements" apparently (I cant confirm this is real), there were reports after the London Olympics that the Flip switch for the 1.4x Converter was poorly placed in relation to the 1Dx Body/Controls on the Camera.
So, who knows, Canon are mind blowingly Obtuse on the matter, this Lens as we know has become the "Mythical Monster", I sincerely hope it will be this year, I have a Tanzania "Migration" shoot coming up in june/July for 4 weeks, I had hoped to have this Lens, I plan now on taking the 300/400 & 600 as I have no confidence Canon will have this Lens available by Mid this year, end of this year ?? Probably, I mean, Nikon have had a reasonable one for 10 Years."
So, it is becoming a frustrating experience waiting for Canon to pull the trigger on this Lens, I do believe we will have it this year, which must be 3 years since it was first "mentioned" by Canon as a Lens in development, the fact that Nikon have had a very good 200-400f/4 in Production for 10 Years, now on it's second Version, and is a big seller for Nikon with Wildlife shooters, seems to indicate that Canon management have been a little slow to the Party, but I think that's Par for the Course in Large Japanese Companies, they seem to get entrenched in a certain mind set & it becomes difficult to shift them. Having said that I spent a month last December in Japan travelling around & it's an amazingly beautiful place.
So, we wait, I have a pre Order in, looking forward to getting the Lens, it'll come I have no doubt, I believe this year, but I'm not planning on having it for my June/July trip to Africa, maybe for my Polar Bear trip to Svalbard in October, maybe.