I still have my EF 70-200 f/4 original! Works great; takes a 1.4x fantastically; takes a 2x when necessity strikes; and slips into a travel pack quite well for what it is. DLO keeps it modern for large and small farm game. But, I do look at the 2.8 side and wonder whether I should get one for the collection. There's an article from Grant Atkinson on the quality of the 2.x combo with the EF 2.8 II (and I presume III) that keeps nudging me. Other priorities first, however.
In my opinion, the extra-compact 70-200 f/4 and f/2.8 RF editions make these long-term road apples or collector curiosities: very innovative for their compactness, yes, but not useful for general bag inclusion at the prosumer level with the lack of extender support (it means more lenses, or swapping for lenses that are aperture compromised in the 70-200 range). I think moreso that they showed off what can be done with the then-new mount, more than anything — while also letting Canon say "me too" for the range. My f/4 remains an excellent 70-200 f/4, a great 98-280 f/5.6, and good 140-400 f/8 (f/9 to milk it). Yes, solid alternatives exist that cover that range, but none of them are f/4 at 70-200. The f/4 EF nicely balances IQ with extendability, weight, size, and cost. If the lens is making money, then I think that the 2.8 achieves the same thing in spades with some nice weekend flexibility thrown in. Unless it's the compact 2.8, that is — then it's somewhat boring.
Nice article, thanks! It's neat to see the EF -> RF evolution in one place.