I’m a 24x24 fan, I've got 3 cameras that shoot square on 135 film (well, four if 126 counts), but I think that for "general" public square would mean a lot of hassle because lab scanning efficiency would drop like a stone which means scanning would be less accessible to people who can't/don't want to camera scan their film at home.
Fortunately that won't be a big hurdle as new 24x24 scanning masks for the most widespread lab scanners like Fuji SP 3000 and Noritsu HS-1800 can be made very fast and at low costs.
There are already some small and innovative companies producing new (and often improved) scanning masks for these scanners. Halfframe 18x24 is also already offered.
Here just one example for such a company and their product programme:
Made by Bobach
bobach.org
Concerning 24x24mm square format in general, I think it could be indeed successful for Pentax to offer a "Pentax 24 square" as a sister model to the current Pentax 17.
Because of the following reasons:
1. The square format has been very popular in photography for decades. Not only in medium format, but also in amateur formats: More than 150 million Instamatic 126 cameras have been sold in a bit less than three decades. And also a high three-digit million number of Polaroid integral instant film cameras, and several million Fujifilm instax square cameras.
The square format has not been as popular as the rectanglar formats, but nevertheless a very significant percentage of photographers like it (and lots of photographers are using both rectangular and square format).
2. "Same parts strategy": Most of the parts of the Pentax 17 can be used for such a Pentax 24 as well. That lowers both design costs and production costs significantly, with improved economies of scale.
3. If Pentax offers a "camera family" based on the Pentax 17 - Pentax 17, Pentax 24, Pentax 35 - it would not also lowers overall costs, but also the total customer base / user base could be increased significantly. It would also be very good from a marketing point of view.
Best regards,
Henning