AdamBotond said:
I don't think it is going to happen in the nearest future, not at F4 at least. I agree however, that primes with built-in 1,4x or even 2x extenders should be really considered by Canon. A 400mm 2.8 with built-in 1,4 and 2x would be a game changer for sports and wildlife.
A
Yes, a 400mm 2.8 with a integrated 1.4x would be nice. But Canon has been displaying a prototype EF 600mm F4 DO at the trade shows for more than a year. I own a EF 600mm F4 which is fantastic but quite heavy. The prototype EF 600mm DO is compact and very hand-holdable. An integrated 1.4x on a 600 DO would be over-the-top good.
I shoot mostly wildlife but the 600mm is also a great lens for many sports and Canon's 2nd most popular lens in its loaner program during the recent Olympics.