100-400 F4 without 1.4 extender, Would be a good alternative to the 200-400 maybe half the cost?
Same constant aperture, and a 4x zoom range instead of 2x for half the cost? A built in TC doesn't account for that much of the cost!
A replacement 100-400 will not be f4 at the long end, unless its bigger and more expensive than the still missing 200-400. There's a need for a lens the size/weight/price/focal length range of the existing 100-400. That means any replacement will be f5.6 at the long end.
(The price will be about double the existing model
)
Lol you're right half the price of a lens that's not available for sale for another that's just rumored is just silly thinking. Of course a built in teleconverter doesn't make much of a difference in price of a lens and there's probably not much extra engineering involved!

maybe they will release a 100-400 NON L lens like when they had the 100-300s