My backup wouldn't it be cool if is, unlike the above reasonableness, a joke: imagining 108 USB hard drives chained to a poor PandaBoard ES, running a fistful at a time: https://plus.google.com/113218107235105855584/posts/BJUJUVBh...
The Marvell ARM chipsets at least have SATA built in, but I'm not sure if you can keep chaining out port expanders ad-infinitum the same way you can USB. ;)
Thanks so much for your words. I'm nearly certain the custom logic boards you mention are done with far more vision, panache, and big-scale bottom line foresight than these ideas, even some CPLD multiplexers hotswapping drives would be a sizable power win over SATA port expanders and USB hubs. Check out the port expanders on OpenCompute Vault 1.0, and their burly aluminium heat sinks: https://www.facebook.com/photo.php?fbid=10151285070574606...