Nikon will at some point have to develop a new DX sensor - "a" meaning there will only be one, because they will need to use it across the DX range and for a long time, in order to recoup the development costs. If that was a 45MP DX sensor it could simply go straight into the Z8II. 

However ... the D500 suffered because although it did offer higher pixel-density versus the 20MP D5 and D6, it did not versus the 45MP D850 when that appeared only a year later, and although a (say) 45MP DX sensor has higher pixel-density than the current Z8 and Z9, it also would suffer if later iterations of the Z8/9 had 80MP or 100MP (DX crops of 35 and 44MP). So a lot will depend on how Nikon expects the Z8/9 to evolve over the next couple of iterations. 

The need to use the sensor across the DX range means cost and suitability for video are likely to be key factors, especially if the predictions of a DX - ie, less expensive - counterpart to the ZR in 2026 are correct. The RED Komodo/Komodo-X use a 20MP Super 35 (27 x 14mm) sensor to do 6K at 40/80 fps, and cost $3000 and $7000, so a 24MP partially stacked DX sensor giving 6K at 60 fps would match well.

I don't think that the entry-level DX cameras will be able to use the same sensor as a proposed high-end Z70 or Z90 (D500 equivalent mirrorless "pro DX" camera). This is because the D500 is a high fps camera with high-end AF and a lot of the users expect top action photography performance which necessitates the use of a sensor with fast readout. Such a sensor would too expensive to use on cameras like the Z30, Z50 series etc. Therefore there will need to be (1) sensors that are affordable to keep camera prices low for beginners and people from less rich countries, and then if (2) a high-end sensor is needed for action photography then it would likely not satisfy the need for high pixel count. (3) A sensor that would give more detail for wildlife and bird photographers in situations where fast action is not a priority would then be the third category, and possible (4) video-optimized sensors fourth. I don't think Nikon sells enough cameras to pay for the development of all these in the DX format in addition to their FX sensors. Nikon's partially stacked Z6III/ZR FX sensor is reported to have a shadow flickering issue which was only partially resolved in a firmware update. It's also reported to produce soft h.265 log footage in the ZR (possibly due to the camera being too small to effectively deal with the heat from more compressed encodings with noise reduction for the shadows). I think Nikon needs to sort these issues out if they want to produce a tiny DX Z camera with a video priority. A Komodo sensor probably requires active cooling and a large chassis to produce the expected performance and these may be incompatible with the concept of a ZR-style camera. I think Nikon should update the current 20 MP DX sensor at some point with something that is both faster and a little higher resolution and perhaps the influencer and youtuber crowd can pay for the development of such a sensor. But it will not likely satisfy bird photographers looking for a D500 equivalent mirrorless camera because of the so many different requirements of these different user groups.

Going down is easy -- getting up again may be more difficult

Yeah 

Its been awhile going down on my knees for a flower shot,
purple crocus.

Zf  Voigtländer 40mm f/1.2

Feeding the capricorn - Z30 & Z 24mm f/1.7

Such fun to be among such magnificent creatures!

Ribe south Jutland
Owner must be fond of red