This is my pure speculation:
The next Z7III may share the same sensor used in Z9 and have no mechanical shutter. If Tower Semiconductor would develop a lower cost, lower pixel (around 30MP?) sensor using the same technology, Z6III could also go without the mechanical shutter. Z5II might be a virtual Z6II, the only model that will still have a mechanical shutter.
Zfc is practically a Z50 derivative with the UI of a film camera, so, there isn't really anything new about the APS-C models at this moment.
The only remaining mechanical part in any full-frame camera is IBIS which may stay for a while, because you would need a larger sensor to enable the fully electronic image stabilization.
I'm not SIGMA fan boy, but, their fp model turned to be a radically forward thinking camera to eliminate all the mechanical parts: the shutter, the IBIS, the mirror of course, and even the dust reduction!