Wood in water is at a constant humidity level. It won't expand and contract with seasonal moisture changes. Wood in your home is subject to all kinds of humidity levels that cause it to expand and contract. No type of coating will create a completely waterproof seal under those conditions.

Just use regular wood with a water alarm and Flood Safe supply hoses for the DW and icemaker.

Marine varnish is the sealant. As hollysprings said it won't stop damage from a flood. A wood floor in the kitchen is possible and will work. Look at all the undamaged flooring in century homes. Take flood precautions as hollysprings suggests. I tore up the kitchen floor and went with hardwood. Sure is a pain saver with all those knee operations I've had.