Nikon could have the Z70 be the first Expeed 8 camera. Especially if Expeed 8 is already done and there is another reason why the Z9II is delayed. It could also allow Nikon to test changes on a lower model if there are major changes coming to Expeed 8. If the Z9II is buggy at what's expected to be a 6k+ camera, people will not be happy. If a 2k crop sensor camera is buggy, people will be much more forgiving.
Personally, it will come down to whether the Z70 will have pre capture raw, a fast enough readout speed for pre capture raw to make sense, and more MP than a DX crop on my Z8. I used the D500 for years for wildlife photos. At the time, it made sense for basically the same reasons above, faster FPS, better AF, and more MP for cropping. Since the D850 we really haven't had a reason to use a crop sensor camera for wildlife with Nikon, but for the right specs, I would consider doing it again.