Well, a7 III and a7R III could actually arrive at the same time, and I wouldn't complain at all about that.
If it was up to me to direct Sony's a7 strategy, we would have:
* a7 III with 24 Mpix and the same AF as the a7R II. Maybe clean 4K, but just leave the current a7 II video (1080p with aliasing/moire) if needed because this one needs to be CHEAP ($1700 at launch, lower if possible).
* a7R III with more Mpix and improvements in all the things photogs care about (AF, flash triggering, that kind of stuff I don't even know about). Not many video improvements because Mpix are not optimal for video and the a7S is the one for that.
* a7S III with 18 Mpix and same AF as the a7R II or III, full sensor readout giving clean 4K at 60 fps, un-crippled slog3 for dynamic range that matches the FS7. 10-bit would be nice but it's not mandatory on the III; it should be there, even internally, on IV, 2-3 years from now.
and..."touchscreen" with AF FD tracking as good as the 5DmkIV / 1DXmkII.
david