Yes, APS-C still sells more, but that market domination has been steadily shrinking and, most importantly, Canon aren't in the same boat as any of the other companies. Fuji buy most of their tech from Sony, so their R&D is lower. Nikon is in a similar boat, they've always bought their sensors and processors from other companies. Sony don't actually make much money from their cameras at all—in fact they've lost money in more financial quarters than they've profited—but they do that intentionally, positioning their cameras as loss leaders, as their real business is selling their sensor and processor tech to other companies (like Fuji), so they don't need their consumer cameras to actually make much money.
Canon don't buy in from anyone and they're not selling their consumer camera parts, either. When they put a camera out it actually has to make profit on the body itself. It's much harder for them to justify making products at those lower price points. Given they've effectively abandoned EF-M, despite selling so many units, it's hard to imagine they'll support APS-C much in the future. At least not to the extent EF-S and EF-M were.
As I've said in the 16mm f/2.8 thread, I do think RF APS-C bodies will happen, but they'll be high-density equivalents to the 7D for wildlife and open air sports shooters, and maybe a video-optimised vlogging camera; I don't think we'll see Canon making APS-C RF lenses, nor do I think we'll see any kind of RF equivalents to EOS M/Fuji X/Sony axxxx cameras. Maybe they'll put out one last M body if development and production of RF continues to be hampered, but don't expect much beyond that from Canon.
If you want a system that is really dedicated to APS-C, you're going to want to move to Fuji who are all-in on the format, or Sony who at least keep producing the bodies, even if they don't particularly make many dedicated lenses. As much as I don't like Canon's fastly-increasing prices, especially how they keep screwing over the UK by charging triple our actual tax rates, I do respect the fact that their business requires them to prioritise the more big-profit products.
To be on the safe side, I'll say both. I was told the (then-coming) lens firmware would fix it and sure enough my 85 worked fine after updating to firmware version 3, but I also already had the bodies on the latest firmware, anyway, so maybe there is some part of the body firmware that does matter and I just didn't spot it because my bodies were up to date already. And in fact I would've updated the lenses regardles, simply because there's no real reason to not update firmware on any lens or body.
I would not expect this lens to come anywhere close to the 400 f/5.6 in image quality, focus speed, or build quality. That EF lens has been a top-seller and 'the' defacto wildlife lens for decades for good reason. The only Canon-mount zooms which match its image quality (they do not exceed it) are the Canon 100-400 mk II, 200-400 f/4L, and now the RF 100-500; all L lenses, all much more expensive and heavier. No other Canon zooms can match it and no Sigma or Tamron zooms have matched it, either. Importantly, its focus is much faster than all the zooms and its build quality is superb; though it does lack full weather sealing, I used mine in heavy downpours and it didn't have a problem, and you don't have to look far to find many other people with the same sort of experiences. The phrase "built like a tank" gets thrown around too often these days and now usually only means "has some metal in it", but the EF 400mm f/5.6L genuinely is a tank of a lens.
The reality of using these long focal lengths is that zoom range and IS are very rarely of any use; what are you photographing at 400mm that you can use a shutter below 1/500th with, and when are you not going to want the maximum focal length? And if you're photographing anything which might move (which is 99% of super-tele use) then your panning can screw up stabilisation systems anyway, even in the panning modes, hence why you'll find many pros just keep the IS off entirely.
A lot of people buy a 100-400 then only use the lens at 400mm with shutters upwards of 1/1000th, rendering the zoom design and stabilisation pointless. The 400mm f/5.6L has remained the standard by which all others are judged because for the purposes these sorts of lenses are most commonly used for, it offers the best-possible optics for the price range, the best-possible focus for the price range, and build quality which is only bettered by a small handful of lenses. (Which this RF 100-400 f/8 certainly will not be part of.)
This new lens does interest me greatly and as long as the first full reviews give it an even just mediocre pass, I'll probably buy one. But I'll be doing that as someone who has moved up through the whole super-tele ecosystem, from the lamest kit zooms to the 400mm f/5.6 to the 100-400s and 150-600s, then on to the really big whites, and now I do want something as light as possible to carry on my evening strolls. If I were in the position where I was contemplating buying the EF 400mm f/5.6 used—so I'm assuming you don't have any other, bigger, higher-end lenses—I would not consider this sort of zoom lens as an alternative. The chances of it matching the optical performance are essentially zero; the 100-500 ''only'' matches the old prime, and there's no way Canon are going to produce a much cheaper, smaller lens like this which equals their premium lens in optical quality. It's very unlikely to match the old lens in focus, too; it's much easier for the larger full USM motor to move a primes' optics around than it is for the 'nano USM' motor to move around a zoom. And we know there's no way it'll match the build quality; it's a plastic, extending zoom that doesn't even have a hood included.
I have my fingers crossed this new lens is good and like I said, there's a high probability I'll buy one myself, but it is extremely difficult to recommend any lens over the old 400 5.6, at least within this price bracket, if someone doesn't already have a really high-quality optic to pair the lighter, weaker lens. The quality of that 400 all-round is superb, on par or better than anything else under the two grand mark, and the fact you can now buy one second hand so cheap and easily resell it for the same price also makes it the lowest-risk lens of its type. When you want quality, portability, a relatively low cost and you only want/can only have one lens, the 400mm f/5.6 has been the king for nearly three decades and probably will not be beaten until an RF 400mm 5/6.L is made.
Buy the old 400 used as you planned, and at worst if you don't like it you can sell it for what you paid and get this new zoom which by that point should have actually been out and been reviewed thoroughly.
Do yourself a favour and, if you do get the 85mm f/1.4L, just buy some extension tubes to do the macro shots with that lens. The two EF 100mm macros, and the RF 100 now, have really strong focus breathing, so by the time you're even at 'just' half magnification they're really more like 85mm and by the time you get to 1:1 they're at only about 65mm. The 85's stabilisation is also more competent than the EF 100mm f/2.8L's (of course the non-L doesn't hjave stabilisation at all) and the close-up quality of the 85 on tubes is better than either of the EF 100s, and by using tubes rather than inherent focus you're keeping more of the focal length, so the 85 1.4 on tubes actually ends up with a longer working distance at 0.5X and larger magnifications than the bare 100s do. This is why a lot of full-time macro pros use the EF 100mm f/2.8L on extension tubes, so they avoid both the breathing and the magnified fringing that happens if you use that lens at 1:1 bare. RF macro tubes right now are bizarrely expensive (nobody should be paying £200 for what is essentially just a spacer!), but when adapting the EF lens you can use EF tubes which are dirt cheap.
I think it'll be a long time before the EF 85mm f/1.4L isn't the best all-round short-tele to use on RF bodies, no matter if you want it for portraits, indoor sports or macro. And I say that even as someone who prefers 100mm over 85mm for most purposes; the EF f/1.4L is just that good and the other Canon lenses are that compromised.
