Having said that I would have no trouble at all making a version of this that’s waterproof! For that though I’d make a PCB and use my own magnetic key switches (Void Switch)…
When I made that keyboard for Chyros I asked him if he wanted it to be waterproof and he said no so I never bothered but it’s not very difficult to do such a thing when your entire keyboard is contactless.
The “key” is to use waterproof connectors or just solder the wires directly to the PCB. Then you just coat the whole thing in silicone sealant (or similar e.g. seal it with epoxy, Flex Seal, etc). The chips don’t care and hall effect sensors will still work just fine through any non-ferromagnetic coating (e.g. any plastic or hydrocarbon-based material).