So, the question is: the Canon 200/2.8 II is not a very common lens - why?
Why is the 100 f/2.0 not more popular compared to the 85/1.8? I see a few 85s on ebay each week, you might get a 100 every 2-3 weeks up there. But they're practically the same lens, size, weight, price, IQ, everything. Maybe it's because if people want the 100mm, they'll sacrifice 1-stop for macro capability and get one of them. Or they'll sacrifice 1 stop and get the flexibility of a f/2.8 zoom.
Back to the 200/2.8.
Basically, what I'm saying is, every lens is a tradeoff, in terms of size, weight, IQ, price, and even if you can afford to buy all of them, there's only so much space in your bag. f/2.8 primes (except maybe the 14 f/2.8L II) are kind of in a "dead zone". They may be cheaper and slightly better IQ than f/2.8 zooms that cover the whole range, but how many primes can I get before I may as well have had the zoom? (for both price and space in my bag).
Zooms sell better to most consumers so more R&D goes into updating them, and the uber-fast primes, f/2.8 is the slowest non-macro-non-TSE prime available, and they're all older than 10 years.
The IQ of the 70-200 f/2.8L non-IS is not *that* much worse than the 200 prime, and for the extra 40% on the pricetag you get the whole 70-199 f/2.8 range. It's also newer and better bokeh. Most consumers accept this trade-off, and that's why the zoom would sell a lot better. The 70-200 f/2.8L IS II just creams them both, and has IS, weather sealing, better IQ, better bokeh, but a pricetag to match.
If a 200 f/2.8 II prime were released today (even a f/2.5 version), with IQ to beat the 70-200 f/2.8 IS II, better bokeh, circular aperture, contrast, colours, etc, and priced somewhere around where it is now (ie halfway between the 70-200 f/4 and f/2.8 nonIS zooms), I still don't think it would sell too well, it's not different enough, I still think most consumers would rather the flexibility of the zoom. If it were f/2.5 it might get a few more buyers, but not enough to justify the extra R&D expense. So I doubt we'll ever see a replacement for this lens, it's just going to fade into obscurity because most people would rather the flexibility of zooms.