Can we create a 1 size fits all rule when the course is being modified in real time from mother nature? But we definitely realize more than ever, the sport has severe risks to the elbow and knee, magnified greatly when your ability to brace, stand firm, (stand still throw or 360), is greatly reduced due to slippery conditions.
I am not talking about a disc landing off fairway, etc, I'm talking about a disc landing in the fairway, in an area that before the tournament started was safe to throw from, but now is a potential career ending mess. Standing in water on concrete is different from standing in water that is muddy, slippery, etc.
I've played in tournaments where the TD would allow players to tee off in the grass behind, or on the sides due to potential slippery conditions. Why not the same thought given for the fairway? So maybe it's as simple as the TD declaring "casual area" (which allows for relief) for muddy, slippery conditions as long as the card agrees & as long as the lie is in the actual fairway. (Not the rough, briers, etc)
So maybe.....a formal rule could be written something similar to... "Dynamic Casual Area - To give dynamic casual area relief due to changes on the course that were not there at tournament start, the player must first declare an unsafe lie. The card then must first determine and agree that the disc is on the fairway and then also agree the lie is unsafe."
That's more than likely what is happening anyway in some scenarios. Again...I'm not going to penalize (score or health wise) a player for throwing a decent drive and then upon coming up to his lie, see the disc in a patch of wet, slippery mud. Never.