And STILL no 50mm 1.4 update, wtf.
We might not need one.
Back in the day there were a lot of factors making even your subject not very sharp, so to contrast with that not-sharp subject, the out-of-focus background had to be far less sharp yet. And, that lack of sharpness of subject meant you often didn't use photos at more than like 4x6" or 10x15cm, so you wanted a background that was obviously blurred even at that small size.
Factors making your subject blurry were: 1) lower quality lenses than we have today, 2) focus basically never being perfect, 3) hand-shake, 4) subject movement, 5) noise at high ISOs (in fact even ISO 100 then was far grainier than ISO 4000 on an R5).
But today, we think nothing of 10x15" photos (a full screen on a medium-large LCD) (25x37cm or so), because of the really good lens quality, focus being nailed, image stabilization, subjects frozen when need be by fast shutter even in low light, and low noise. In this environment, even 50/1.8 gives you a lot of subject pop. And while your subject is far bigger as you confidently display bigger images, the background is likewised magnified making even 50/1.8 bokeh quite obvious.
Also, that large image we now share around all the time means that if DOF doesn't cover your subject's head it will be really obvious. In the days of small images no-one would notice. That means you may need to use f/4.0 or something now where you'd be able to get away with f/1.4 in the 90s. So opportunities to use a lens wide-open are significantly lessened.
Further, with an f/1.4 (or even 1.2 or 1.0) lens is not using it wide open exclusively. You take a LOT of shots at f/1.8 to f/16, and those shots aren't night-and-day better than the 1.8. (The RF1.2 may be usefully sharper at f/1.8 but I have no photos with it that would be keepers with the 1.2 but would not be keepers with the 1.8. And at f/8 or so or numerically higher, all lenses are pretty much the same.)
Finally there's the question of which lens design you'd use. If it's an old-school double Gaussian, it's not going to be much if any sharper than the f/1.8, which hardly differs from Canon 50/1.8's of the early 1970s and earlier. The EF 1.0 1.2 1.4 and 1.8 were all double Gaussian designs and frankly none of them were that sharp, though in other respects they were pleasing and predictable. If instead an RF 50/1.4 were a new-school design like the RF50/1.2 or a few other ultra-sharp modern lenses like the Otus or the Leica 50/2 APO ASPH, then it's going to be far bigger than the 1.4 of old even with its extension tube, and heavier, and pricier. I think Nikon has a modern 50/1.4 now that shows it can be smaller than the RF50/1.2 and usefully cheaper, while usefully sharper than an old-school design, so such a lens can clearly be created, but I don't think it will be as cheap OR as sharp as you want. But arguably if you're OK with big weight and size and price, just get the RF50/1.2 that's been around since day 1. If you're willing to sacrifice some IQ for better size weight and price, just get the RF50/1.8. Again how valuable is it to get that extra 2/3 stop?
My personal experience: I had all EF 50's, so I admit it's nice to have them all on hand. But I only used the 1.0 for special projects. I usually used the 1.8 MkI for unplanned shooting as the camera was always in my backpack, and 1.4 but later 1.2 for planned shooting. I don't think I really used my 1.4 after getting the 1.2, even though the 1.2 wasn't great: the 1.4 just wasn't usefully smaller or lighter. And weirdly, though I preferred the 1.2 over the 1.4 when I had both, I actually kind of wish I hadn't bothered with the 1.2. Once I had it I used it but it wasn't worth getting, really, once you offset that slight extra ability with the trouble of buying it, testing and getting to know it, then selling it.
I'm not sure who will be convinced, but that's how I see it. How often does anyone really absolutely have to have that f/1.4 and f/1.6 shot, but doesn't want an f/1.2 shot?
I had the RF50/1.2 and just wasn't using it and it was too big to always have on me. Now I have the RF50/1.8 and since it's always in my backpack I'm taking a lot of images with it. And while the MTF chart makes it look like only a modest performer, my own tests show it's really quite good enough for my usage. I could see buying another 50/1.2 at SOME point--it was a great lens and I sold it to buy other toys--but I never think about it, much less a 1.4 that might not be as good.
It's the only non-native RF lens I use. On the SLRs, my 35/1.4 was unused as "too normal" while the 24/1.4 was unused because "too wide."
