The problem with any type of minimum square footage is that as soon as you codify a hard-and-fast rule people will work overtime to find a way around it.
We had rules for Bathrooms...people invented 'Powder Room'.
We had rules for Kitchens...people invented 'Break Room'.
As soon as we set a lower limit of 12 sq.ft. for balconies...people will either invent 'exterior viewing area' or find a way to build them to be 11.999 sq. ft.
IMHO, that's why we will always need 90.4; so the AHJ can catch folks who try to slither through on a technicality.
