Canon has done a great job of filling out the supertelephoto options for the RF mount, but there is one glaring omission in the line-up thus far, and that's an RF version of the EF 500mm f/4L IS USM II.
Canon has historically upgraded the 400mm f/2.8 and 600mm f/4 lenses at the same time, and done the same for the 300 f/2.8 and the 500 f/4. With Canon recently launching the RF 100-300mm f/2.8L IS USM, we can see that Canon is trying something new for shooters of the 300mm f/2.8.
We have had a lot of conflicting information this year about supertelephoto zooms. The RF 100-300mm f/2.8L IS USM turned out to be correct. So what about the 500mm?
The most consistent bits of information that we have received suggest that the RF version of the 500mm will also be a zoom in the form of an RF 200-500mm f/4L IS USM 1.4x. With the TC engaged, you'll get a 280-700mm f/5.6L IS USM.
Size and weight will be similar to the EF 500mm f/4L IS USM, which is about a pound lighter than the EF 200-400mm f/4L IS USM 1.4x.
Pricing, I think it's safe to say we'll be getting another five figure lens from Canon. We can also expect an officially announcement later in 2023.
Personally, I will stick with the 600/4 over the 500/4 (practically for my typical use, it's really 840/5.6 vs. 700/5.6), though if the R1 comes in with a pixel density high enough to obviate the extra 140mm (which is reasonably likely), I may consider swapping my 600/4 II for this rumored lens if it becomes a product).
it will be interesting what Canon engineers can develop and design here...
But not for my use :p
On the other hand, they could opt for a compact and lightweight 500/4 prime, and throw in a couple of marketing "features", although I'm not sure what they would be.
Either way, Canon has shown that it wants to offer features that "lift" RF lenses above their EF nearest equivalents, so we can be sure of something exciting.
At this point I’ve gotten over a decade of use from the 600/4 II, and as yet there’s nothing to swap it for.
When you say 'price hikes for the other Big Whites', what do you mean? The RF 400/2.8 and 600/4 are the exact same price as the EF MkIII versions (which makes sense since they're basically the same lens with a bolted-on adapter). The RF 800/5.6 launched at ~40% more than the EF 800/5.6, that's in line with the 100-300 vs 300/2.8 II, but the EF 800/5.6 is a really old lens that never got the MkII/MkIII improvements the EF Big Whites received.
I think your estimate of $20K is way too high. Not that $14-15K is a bargain...
I currently shoot the 500 f/4 II. This lens would end up in my bag. Now or later depends on price point and how rich I feel at the moment.
I also recall rumors of a 500 mm f4.5/f5 DO lens being test as well and wonder if Canon is going to use DO in this lens to keep weight and dimensions down. A 200-500 mm f4.5 DO lens with 1.4x TC built-in would be a very interesting addition to Canon's lineup.
I recall on the failure for the 500mm III to appear, the reasoning cited was that the weight improvements weren't enough of a difference for the smaller lens. The primary benefit of the 600mm III over the II was the weight loss (coincidentally, I took delivery of a 600mm III this afternoon to replace the Mark II I'm about to list. I'm, of course, making the upgrade for the weight.)
I'd be disappointed if we didn't see a new 500 f/4 prime, as that was our hope that we'd actually get a new optical design in a big white. We haven't had a fresh design that improved optical performance in more than a decade. I appreciate the Mark IIIs did improve things significantly from a usability perspective. Perhaps I ask too much for IQ improvements. Seeing as Nikon and Sony's more recent designs have roughly equivalent image quality as Canon's probably means they're all designing toward a common set of limits in physics.
Neuro and I have been rocking the same Mark II lens for a long while, both not seeing a good reason to change. I finally fell to the Mark III this week because I found a really good deal on a used one, and I figure now's the time from a depreciation curve perspective. Interesting that he's considering the theoretical 200-500 f/4 as his path. If light enough, that could make sense, especially if it had the internal TC.