While the idea seems good. Doesnt seem so practical in real world.
Say you have watercooling..Long as when it leaks, it doesn't touch any:
pci-e slots, ram slots, IO slots, pins, fan headers, USB headers, power headers, etc.. you are OK.
Waterproof everywhere but where it connects to, or has something, isn't very waterproof at all to me. I still see it failing 9 out of 10 times due to water leak, or condensation running down.
Now make each connector sealed in some thin split rubber dome or slit that connectors can pass through, then its more water proof