I'm sure the current market for glass plates must be really tiny - but it is surely a bit of a self perpetuating problem... If it isn't possible to buy glass plates then the only people using them are the people making their own, quite a commitment. If glass plates were available again - might it encourage a few people to dig out the Thornton Picards, Sandersons and Rochesters and give it a go? I certainly would. Is it possible that demand may grow.... from really tiny to, er, just fairly tiny?

Could this ever be enough to tip the viability balance?

I wonder what is the most common plate camera out there? Half plate, I would guess. Would an experimental one off coating of, say, FP4 onto half plate be feasible just to test the demand? I wonder if the reaction might be similar to the ULF project, with enthusiasts putting a few boxes in the freezer in case they never get that size again and keeping their fingers crossed that they may get whole plate next year?