Good question. I'll ask one in return. How many have it on the cuff? How many have one, or the option for one, on a heel of the suit? They are out there.
I actually gave this some thought before I went to sleep last night and came up with the following questions. As a dry suit instructor, does it matter? As a new dry suit diver, does it matter? It shouldn't. In fact it should not matter to any competent diver.
As an instructor I should be able to teach any of the locations. A new drysuit diver would not be confused if that is all they ever learned with. A skilled and experienced diver could easily adapt.
Cons to having it on the right shoulder. Have to raise the right arm and the inflator on the left. Is that big deal? Not that I can see if the right amount of gas is being used in the suit and the BC. What else? It;s different. So is a BPW from a jacket BC. A rescuer would have to look for it. Yes, and? Like they would not think to look if they didn't find it on the left. How many rescue classes even think to cover a drysuit diver? All should but I bet they don't unless all are in drysuits.
I thought of some pros as well. It would make getting my suit off and on easier since I usually don the BC right arm first. No getting hung up on the valve. It would make it easier to get the BC off. Again not getting hung up on the valve and having lots of slack to work with. I could also keep my compass on my left arm with the bottom timer level while I raised the right shoulder to dump if I had to vent the suit. Maybe I should have my next suit done that way? Would not cause any issues I can see.