Inverted doubles went out of style in the US (for good reason) somewhere in the early 1990s.
What were the good reasons?
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As someone who enjoys exploring different equipment configurations without bias I am always intrigued by real vs perceived issues and the forces that form conventional wisdom. Three artificial forces currently at play in diving (IMO) are standardization, the law of primacy and the use of equipment required for the most committed forms of diving for all forms of diving. I say artificial because, while they may provide a good platform for individuals or agencies to build safe diving practices on, they are not inherrantly needed for safe diving itself and are often taken out of context. When one chooses those parameters to assess equipment needs there can only be a very limited number of options left available and many viable choices are dismissed without otherwise valid reasoning.
Standardization is a great idea within a team but one has to realise that it also stiffles creativity and one has to understand by who, and for what reason, the standards are being set.
The law of primacy may exist but it is often misused as a way of discouraging exploration. It's pretty tempting to turn "that which is learned first is learned best" into "don't confuse yourself by learning anything different". Personally I believe that the more tools in my tool box, the better; and exploring different configurations allows me to be more adaptive. I place a high value on adaptiveness although I will admit I am more a generalist than a specialist in matters relating to SCUBA which skues my thinking somewhat.
Bottom up or "every dive is a cave dive" thinking means that many viable OW configurations are dismissed because they will not be optimal within the most committed types of diving. That's ok if one subscribes to that form of standardization but it also throws a lot of babies out with the bathwater.
I'm not bashing any agencies or philosophies btw, I actually have a lot of respect for the strength of their regimes, but I also recognise when those same regimes may stifle otherwise workable applications. I also appreciate others challenging my ideas as a valuable way of testing and illuminating the weaknesses in my POV (which, on rare occasions may happen... theoretically).
On a practical note regarding inverted tanks: I find it interesting when one worries about valve damage. Inverted divers worry on the boat and valve up divers worry during the dive.
