Inverted tanks have been used over the years. Even today, you can buy special brackets to protect the valving of inverted tanks.
The old Scott Hydropac from the 50's had inverted tanks, and 2nd stg regulator mounted on a full face mask, in other words, the first single hose regulator. The design was an adaption of the fireman's airpac, made by Scott of course. Then, there was USD's USD-1 made in the early 70's. It used inverted triple tanks inside a plastic fairing. The shut off and reserve could be reached as easy as your back pocket. Going back to the beginning, Cousteau's team used triples which, although not inverted, had reserve valves mounted on the bottom of double ended triple tanks. The BSAC divers from the 50's used inverted tanks and a double hose regulator mounted on the chest. There is the current production AGA Divator which uses inverted 4400 psi tanks, etc. They've been around since the early days. There are others.
Inversion could be the second cogent argument for the DIN valve. A DIN would stand up better to being banged on deck. The first argument had to do with being banged on an overhead. Same difference.
Raising these questions might rouse some DIR guys to get stroke conflicted. They know what they know. What can you say to someone who wraps a 7 foot hose around their neck? They might try to wrap it around MY neck.
