Here is the problem with sinker-wood: Increased density and weight.
Once the wood sinks in a river or lake, microorganisms invade the wood, mineralization occurs, and other processes (which I don't claim to understand). But the end result is that the wood is harder and heavier.
I hear wood dealers tell enthusiastic journalists (who seem to love writing articles on how great salvaged wood is) that this wood is tonally superior for musical instruments. I laugh when I hear this, because it is simply not true.
But I am only speaking of using sinker wood for tops!!!! The top should be light and stiff, not heavy.
For backs and sides however, I have used sinker-wood (maple and cypress) inumerable times. The maple was submerged in the Fraser River here in B.C. for decades. It was harder and heavier than fresh sawn bigleaf maple. The cypress I used was sunken in the ocean as part of a dock piling. It got so hard that when I finished cutting a block of it my bandsaw blade would cut no more! Fresh cypress is soft and cuts like a hot knife through butter.
But for soundboards I see no advantage to using sinker wood, only disadvantages.