It might have been Elmer in the 1930's, or at least another contemporary archery author, dismissed the idea of water seasoning. The thought by contemporary bowyers at the time was it made bows with inferior cast, compared to air dried. The process lasted a couple of months, usually in a flowing stream(rather than still water like a pond). A very different process to +20 years or more of submersion.
Long term water seasoning, as mentioned in the original post, may indeed change the properties of wood, but its unlikely to be for the better in terms of performance with bows. Remember the Mary Rose bows that were salvaged around the late 1970's , early 1980's? They were in immaculate condition, when cleaned. The problem is they nearly all broke when being shot. Replicas were instead made to test the design and dimensions of the bows. The sapwood is likely to have deteriorated on the yew. Whether the heartwood had changed, I haven't heard any mention either way.
If any timber might work with the submerged treatment, osage would be the best candidate. Locust would be worth a try too.