I'm a little surprised that the obvious point about the square having to be less than 23x23 to fit in the circle didn't come up earlier. Maybe worried
But let's not forget that the square picture would not be the only output. There would be at least three formats to choose from without flipping the camera, I can easily see how there could be five. Or six – why not have a circle? Fisheyes have been doing those all the time.
I could also see that at least a raw shooter would have the option to choose the format while post processing.
If you combine this with probably doing away with the pentaprism entirely and thus not having to worry about the bigger mirror etc – I think it looks quite feasible. If it has an improved AF-system I will get one.