The long waited Canon EF 200-400mm f/4L IS USM Extender 1.4x lens now seem got a date for release. It is said to be released in this Fall.
Previous rumors said the delay of this lens is due to the design and functionality, now seems Canon had set the design.
The weight of this lens is pretty close to the EF 600mm f/4L IS II.
The price of this lens would be over $10,000 as rumored before.