I've started building my own cases for just that reason. Cabinets take up too much room. If I had the room I'd collect those too though. There's been some very cool designs over the years and some of the lifts on the treadle cabinets are just amazing.
I don't think door skins have quite enough bend in them to get a true bentwood case out of them. I have a little bit here, I might set up a jig and see how far it goes before it gives out.
Bentwood cases are pretty but they have their disadvantages too. Due to the tension on the wood those bends that we admire so much can start cracking over time. I've seen it on a lot of furniture with bent veneer surfaces and my White bentwood case has that problem too. But then 50 years from now I won't be here to see it.
I think it would be difficult to hit a price point that the market would bear while still making enough money to justify the effort of making the cases.
Rodney