In another discussion I said that very thing. In fact, according to Photons to Photos, the two sensors are identicak in performance above ISO 400. For some reason, the older BSI sensor is a little better (dynamic range) below that.

Ive been trying to learn if it is easier to stack and bond three layers (it's done at the wafer level) or grind off the back of the two layer version. I'd think eliminating the grinding operation would be a good thing.

The benefit Sony claims is that the photodiode sites are larger on the newer sensor. That does sound like a plus...certainly in the context of UHH lore.

Once one dispenses with all the jargon the decision comes down, not to price. But to results. I have a Z6 and use Z lenses exclusively. My particular interests are portrait and street photography. I don’t use video and I don’t use burst. I don’t even bracket. I do some sports photography but find that my D500 is made for that genre. The three factors to consider are price, want and need, the latter based upon the nature of one’s photography. Am I missing something or should I run to my nearest camera store and put my name on the list for a Z8?

The storied z8 has finally come about and has everything we hoped it would but here is a question: How much difference does the stacked sensor make? I currently have a z7ii with the mpx. being the same as the z8 am wondering if upgrading would be worth it. Yes, the eye detection is better on the z8 with it being able to detect birds, and even airplanes vs. the 7 which only detects people, dogs, and cats. I do so little with birds, the eye detection alone is not worth the difference. So many of the great reviews really hit on the video capability of this camera and my video usage is 0 (zero). It looks like it has the best video capabilities of the big three with only Panasonic being a competitor in that area but again, I don't care about video. If a stacked sensor is a considerable improvement on the sensor in the z7ii, it will definitely be a factor in whether to upgrade or not. I was hoping the 8 would incorporate the 61 mpx. sensor Nikon has been testing to make it more competitive with Sony's 61 mpx. body. That would definitely be added to the equation. That also tells me that with them holding back on that sensor, to look for a new Nikon flagship to be in the works -- an upgraded z9 with improvements in eye detection and a 61 mpx. sensor -- call it a z1. My guess is that it would come in at around 6500.00 and would eventually eliminate the z9 from the lineup.

TheZ8 does offer quite a few improvements over the Z7ii, expeed 7 vs expeed 6 processor, 20FPS vs 10 FPS, huge buffer improvement over the Z7ii, better low light AF sensitivity of -7.5EV vs -4EV, and more. Whether you need these or any of the other features the Z8 has that the Z7ii has are totally dependent on what kind of photography yo like to do and shoot. If you don't do any video, do mainly landscapes, cityscapes, family, then the Z7ii may be the right camera for you. You said you don't shoot birds or do video, so those features won't matter too much to you, although they both offer huge improvements over the Z7ii in those areas.

Here are a few video links that may offer some more insight and answer your questions and help you decide.

Steve Perry - https://www.youtube.com/watch?v=fak6fQetpDA&ab_channel=StevePerry

Matt Granger - https://www.youtube.com/watch?v=437aCOqaXMs&ab_channel=MattGranger

Ricci Chera - https://www.youtube.com/watch?v=-Q2N4BRBDMA&ab_channel=RicciTalks In this video he mentions the difference between the Z8 stacked sensor and the Z7ii sensor... they are not the same. The Z8 sensor reads out 12X faster than the Z7 and the Z7ii.

Photography Life - https://photographylife.com/comparison/nikon-z7-ii-vs-nikon-z8

Hope these help.

Personally I think the Z7 II is a very under-rated camera, and while I am also sure that the Z8 is a fine camera that adds features (especially video features) I also suspect that Nikon did not go with the 61Mpx because the lower Mpxl sensor was probably better for video.
This is the supposed successor to the vaunted D850, which was and is a superb camera (albeit not so much for video) When it came out it had the best of everything Nikon could offer.
To be the mirrorless successor to the D850 I would have expected that they would further bump the pixel count.
They didn't.
I am sure the Z8 is a great camera, for the purposes you describe it does not seem to be to be an urgent upgrade from the Z7II. If you shot a lot of video, my opinion would be different. If I were you I'd stand pat for a while, maybe buy a lens you always wanted.......