"If the Z8 can do 15 fps capturing raw files, why can't the new C15 function do the same?"
C15 is a pre-release capture option, while the regular 15 fps is a normal release option. The difference between the two is this: pre-release capture uses the image sensor in a video mode, where the bandwidth and rolling shutter attributes are different.
When a Z8 is in normal still photography mode, the image sensor is subsampled to provide the focus/viewfinder stream, so it can't be used for pre-capture. Video modes, however, work somewhat differently. They have a completely different bandwidth and rolling shutter impact and perform the focus/viewfinder stream from the video stream. (And this is the reason why 120 fps is 11mp: it's a subsample.)
So why can't the Z8 pre-capture in 15 fps video mode and then continue upon shutter release press in 15 fps still mode? That's probably because there's a timing implication in switching between the two modes, and the sequence would not align in time properly (i.e. you'd miss some small amount of time right at the shutter release).
That said, it's unclear to me why we can't get a pre-release capture function with High efficiency raw, as that's really an H.265 (video) derivative, and should be able to be created with the sensor in video mode. I suspect that this is an example where the EXPEED7 chip got locked into stone prior to Nikon figuring out how they would do pre-release capture, and then Nikon discovered that there were issues that prevented certain data pipelines from occurring.
Pre-release capture is one area where I'm expecting changes when we eventually get to the next generation of Z System cameras.
"With the introduction of the 16-50mm f/2.8 DX VR lens, will we get a higher-end DX camera body?"
I think that is still improbable. The FX line sits pretty much at the next price point up from the Z50II, so any Z70/90 type of camera would now be competing with the Z5II through Z6III. What's in it for Nikon to do that? No clear volume gain, for sure. Thus, I tend to rule out a move to a new 26mp DX camera with substantively more capability, and it wouldn't happen with the current 20mp sensor.
Okay, so what about the 40mp APS-C stacked image sensor Fujifilm uses in the X-H2S? That might produce a Z90 to go with a Z9II, and justify being in the US$2500-3000 range. That seems more likely to me, but the truth of the matter is that Nikon's own hesitation (twice) in making top-of-the-line DX cameras coupled with Fujifilm's now marginal sales on the X-H2S says to me that the top-end DX upgrade opportunity might have been lost. Moreover, there would still be missing lenses. In particular, you'd want to see a 300mm f/4 PF VR S in the Z-mount, plus perhaps a 50-150mm f/2.8 DX VR.
Nikon's at a critical juncture with DX. The Z50II re-invigorated the DX line enough that it shows in Nikon's financials. The most likely scenario at this point would be a Z30II and ZfcII, with the former more mimicking the ZR. However, that would need to be matched by new high-end demand in FX (i.e. the Z9II generation starts), as otherwise it just lowers Nikon's average selling price and puts them back into chasing volume.
"Now that Nikon's hit 50 lenses, is that all we're going to get?"
It is curious that Nikon wasn't asked that at the shareholder's meeting and hasn't addressed the question publicly in any way. I'm currently tracking three new lenses, one of which is a II version of an existing lens. And let's not forget that Nikon has already said that they will produce Cinema lenses. So the direct answer to the question is "no."
I think the bigger answer to this question should be obvious, though: Nikon is an optical company. To stop making new lenses would be a contradiction to their core expertise. Moreover, Nikon's been investing heavily in remaking their entire lens production facilities, with the two new Tochigi, Japan plants expected to be operational in 2027.
Historically, Canikony (and originally Canikolta) have all produced a broad lens lineup, but that lineup never really went beyond about 60 current lenses in a mount (the number offered went higher for Nikon as they retained some production of film SLR lenses for a long, long time). Each time they approached some cost effective ceiling in number of lenses produced, we saw two things happen: (1) reinvention of existing lenses, making them better; and (2) exploration of new, interesting optical problems to create unique lenses we didn't have prior (e.g. tilt-shift, phase fresnel, new element types, etc.).
This time around, though, we have the Chinese nipping at Canikony with a wide array of competent prime lenses. It's only a matter of time before that expands to zooms and what I call exotics (we've already seen nibbles at both). That changes the mount economics for Nikon. Right now Nikon is still forecasting growth in unit volume and market share over the next six months. But I also note that Nikon's numbers all center around CIPA numbers, which doesn't include the Chinese companies. The overall Z-mount lens sales has actually grown significantly in the past two years, partly fueled by low cost Chinese primes. This is one of those good news, bad news situations for Nikon, as it is the body sales growth that's driving this, but at the same time, Nikon is facing substantial competition in the prime lens market now.
Finally this: behind the question is some implied fear. You don't ask the question if you think Nikon is fully healthy and operating as normal. At the moment there's nothing to fear. Nikon has navigated this problem before. That's typically turned into some of the best new lenses Nikon has ever done. Again, they're an optics company at heart. They'll want to show that they're still 100% on top of that game by creating unique and exceptional lenses.
Moreover, there's this: Nikon made their first 24-70mm f/2.8 in 1999. In the twenty-five ensuing years, they redesigned it four times (original D, G, E, Z, ZII). The current version is exceptionally better than the first, and clearly better than even the most recent. Nikon's not going to let others usurp their position on key lenses, let alone exotics. The competition they've had in the lens market for so many decades has only made their most recent versions better, and I see nothing changing about that.
