Canon Still Working on New 800mm Lens [CR1]

We've been told over the years that Canon is working on a new 800mm lens, which is likely true and such development does in fact take years. The current 800mm f/5.6L IS has been a tough sell since the launch of the EF 600mm f/4L IS II, as the image quality you get from the 600mm lens and a 1.4 III teleconverter is generally considered better and you get an 840mm f/5.6 lens.

We've seen patents for a new 800mm lens in both DO and non-DO forms and thought we'd have seen a new one by now to at least match the materials and performance of the 300-600mm lenses that were launched 5 or so years ago.

An unknown source says Canon is developing an 800mm f/5.6L with a 1.4 TC built into it like the EF 200-400 f/4L IS 1.4x., which would give you an 1120mm f/6.3 when the teleconverter is put in place.

We're not sure how many big white lenses Canon is currently selling, but it feels that there may be some market saturation for the lenses and we're not sure there ever needs to be an 800mm replacement. It's going to have to offer something quite unique to get current owners of big white lenses to get on board.

We wonder if some sort of a supertelephoto zoom above 600mm would be doable and cost effective.

An appropriate amount of salt recommended for this one.