You would also need to protect the PCB. Look up "conformal coating" to find info on DIY-able protective coatings.

GLWGB!!

Any update on this? Still very much interested!

The Kailh Box switches are the first to come to mind. The slider pushes onto a lever on the side of a box, and the mechanism is inside that box, separate from the compartment with the slider. That is supposed to make them more resistant to dust.
However, I dunno if anyone in the community has actually put that to the test.

The Kailh Box also has a shroud around the stem supposed to also make it harder for dust to get inside the first compartment.
Switches from other manufacturers with just a stem-shroud have also been marketed as "dust-proof" without being significantly different on the inside than a standard MX-type switch.

BTW. There are also some vintage boards with Cherry MX (or clone) that has like a fitted rubber or plastic sheet to protect against dust and liquids (colloquially called a "keyboard condom"). Those sheets would only fit on regular stems: not shrouded ones.
I've had one with a silicone sheet but it impaired key feel considerably, but I've seen police car keyboards with a thinner sheet.
I wonder what the best way would be to make one yourself. Perhaps 3D-print a mould, lay a sheet of plastic bag material and gently use a heat-gun? SIlicone would require a two-part mould, I'd think. Silicone could be thickened to be brushable, but the result would be stiffer and uneven.

Is anyone aware of any MX compatible switches that are legit dust proof?  I am probably going to be getting issued a tablet at work for a new-ish safety program.  The issue is I hate typing on a tablet sized touch screen.  So, I am wanting to swap the Cherry switches on my JD40 and my GH36 to dust proof.  The reason I need dust proof is because I work in one of the largest cast iron foundries in the US.