It is about one-shot. Stitching yes. But 3:2 is an inefficient use of a mount vs. 4:3, but of course efficient for Sony to cut it down to 35mm, crop MF formats. And stitching gets annoying with 36mm as it means you need to make three shots with an STC say for a pano in pano orientation. 36mm means more stitching is needed to get to a same FoV than with the IQ4. Its nice that you can shift the IQ4 left right 18mm on an STC in portrait mode and have a 2 shot stitch in PS. The more stitches you need, the more risk for artifcats. That's why for critical work (e.g. gallery print without errors) its easier to have a nice one shot file where 4:3 is a lot more flex.
This means for non static - people (environmental), aerial, scenes with people, wind, water, etc. you lose format flexibility in 3:2. I already can see the dealer's spin on it, with crop being still higher res than previous gen full frame, but besides one-shot flexibility you also lose a tiny bit of perspective differentiation vs. crop MF.
4:3 is also reminiscent of large format, widely perpetuated in fine art. I like the amount of foreground and sky one gets in environmental full body portraiture for example vs. 3:2 which looks like *cheaper 35mm". It is as you say subjective.
I hope they can get a custom order going 54x40.
There's also still catch up potential with portra film re DR. 1 to 1.5 more stops in the highlights would be awesome.
One side aspect of a 3:2 ratio would be that shorter focal lengths get longer via crop, meaning if your favorite focal length was 40 it is now 32 and 23 becomes the new 32, etc. 90 becomes even more longer in practice etc.
So it could be a bit of a revival for the 32, 40, 50 core of HR rodies plus 43 and 60 XL and 90, 120 being less used.
The poll is super clear in that people want 54x40 - I hope P1 takes note. They have the clout to commit to an exclusive order of a few thousand units over the next years across aerial, repro and photo., I hope.