Unfortunately this is like a high end Commodore64: it starts simple but soon you have a rats nest of cables separate power for all the external devices. I want less cables not more. Also, I don't think thunderbolt cables can be screwed in, so you run the risk that a cable could get tugged and pulled out.
I'm thinking like an 8-drive chassis, and maybe 3- and 6- slot card cages, rather than lots of single-purpose external devices.
Rats nestery need not be too bad. Thunderbolt from the Mac to the drive chassis, then thunderbolt daisy-chained to the PCI card cage chassis. Power cords for the drive chassis and the PCI card cage chassis, if they can't be powered by thunderbolt. (Naturally, how ratty the PCI card cage gets would mostly be determined by what cards it contains and what are plugged into it.)
Not sure what the cable length limits are, but it might be possible to spread these out a fair distance, especially once optical-based Thunderbolt happens. Being able to put the PCI cards close to what they're connecting to, with just a single Thunderbolt cable running back to the computer, could be a cable management win, versus snaking multiple cables to a computer.
I'm sure someone could come up with a screw-in variant of Thunderbolt, but even so, I don't think Mac Pros have any screw-in connectors as it is, apart from the video cables screwing into the video card(s).
