I'm not so sure about the bullet-proofness of water-logged old cypress. Living and breathing cypress is pretty cool stuff. We have all seen wall clocks and tables made from cypress for sale alongside our Florida highways. For years these were some of the best tourist traps!
As tough as lignum vitae is (and I don't think anyone can argue that who knows anything about it) it still gives me (and the Randall shop) fits. Cracking is common on my handles. I have probably used more LV than anyone on Randall knives, with over 100 made and ordered. I would be cautious on the cypress.
Besides: I don't know where one would go about locating some that had been properly cured, dried and stabilized. Could be a real bugger to complete the build..."BUT"...(I know, I know)...I don't care what we build.
Keep those ideas comin' folks!
Best, Capt. Chris