This lens should be under $4k. I guess there are people willing to buy it anyway, and so Canon will charge what the market will bear.
I don't know. It is a considerably more complex lens to manufacture than a 500mm f/4 or 600mm f/4, offers 200-400mm zoom at a constant f/4, and up to 560mm @ f/5.6 with the 1.4x switched in.
Besides, at $4k, there'd be no room for the 100-400 II!
I agree. Maybe they will over-produce it and the next round of Canon lens rebates will include a $8-10K rebate on it
Or, they want to put this out so there so that when they finally offer an updated 100-400 zoom the $5K they charge for it will look like a good deal!