Well, you kind of have yourself worked into a box FE, because you know the ST tire sizes are unique to ST tires, so any deviation towards an LT tire puts you in a tire size not listed on the side of your trailer, and no trailer manufacturer is going to stick their neck out and give you written acceptance of your alternative tire when the tire manufacturers keep telling them that an ST is the RIGHT TIRE for the job.
When you drive in traffic, do you follow the speed limit sign to the number or do you follow traffic? Regardless of what the laws or standards are saying, if the tire success comes from those that switched to LT, then at some point a guy just doesn't care what his sticker says anymore or what the manufacturers say and he is going to do what works.