These are the comparisons I was thinking about. The 200-800 at $1900 is going to be tough to beat for those of us who imagine using a 400+tc. I think the value proposition might only make sense for those who want to shoot at 400mm. This gets you there at a light weight sacrificing one stop of light vs the 400 f/2.8 (a $12k lens) at a lower cost. But the EF 400 DO is still $6,900! I just don't see how the RF version can support even that level. When the EF version came out, effective 600mm at f/8 was the sweet spot achievable with pretty good glass in the $2k range. The 400 f/4 with extenders would get you 560 at f/5.6 or 800 at f/8., thus giving it a reason to exist beyond 400 prime shooting. The new RF 800 at f/9 for under $2k kills that.
All of that is to say, EF price suggest $8k would reasonable, but I don't see why anyone would buy it at that price. You are down to 400 prime shooters who are pros, I don't think they are going to give up the subject separation to save $4k. But I'm not a pro, so I'll leave it there.