I've seen a few 500mm cases, but yes, none that take that many drives. It's for a lot of storage on a budget
I've seen and like the Norco 4220 and 4224 to put my spares in and rack up with shiny new drives, but when I looked to see if I could find much the same thing just shorter (as it's for home use and so don't need the space for EEB boards) I couldn't find any. It would just be nice to fit that kind of capacity into a network-depth pedestal cab.
And I would go for a separate 1U server and DAS but again there's the issue of cost. I know DAS units typically come up shorter, but the MD1000 is typically £500+ with empty caddies, even second hand. Unless you know different..?
I mean, if it was less then I would definitely consider one.