I feel like we're kinda arguing about whether heritage blue is better than Sand color when Toyota could just have both colors. Everyone wins.Cleanability benefits of softex over cloth seats is clear. This is why I've seen it in multiple Toyota car rentals that I’ve been in. A quick wipe down of the seats by the staff and they are good to go for the next renter.
As far as the cooling problem man I’m not really sure what else to say. Certainly worse in summers but I think it’s simply due to the fact softex isn't breathable. Even with A/C on it eventually gets hot uncomfortable and sweaty wherever you are in most contact with the material. There's just no airflow to fairly large surface areas of the body. Resulting in swamp ass (and back). Maybe some are more sensitive to this? But I am confident I am not alone with this issue with softex.
It does seems like seating material should be one of the easier things to implement customization on across trims.
Frustrating part is that Toyota is the ultimate master of individual vehicle mfg. If anyone can make this happen without a big cost differential it's Toyota.