Interesting article, however, not new information. This mode of operation, to my knowledge, has been assumed since the discovery of the site.
With regard to commercial applications, the measure of the effect of water density on criticality is called Alpha T. A negative Alpha T implies that a decrease in water density promotes shutdown (as described here). A positive Alpha T implies the opposite. All US and Western commercial reactors have always, by law, been required to have a negative Alpha T. The Soviet RBMK reactor (think Chernobyl) OTOH had a positive Alpha T.
The principle described therefore has always been a bedrock of Western commercial reactor design.