The Seagate Free Agent GoFlex Docks were an excellent product, allowing interchange of hard disk drives and connectivity protocols. They made USB 3, FireWire, and even NAS docks for these hard disk drives. But the connector is standard SATA and could be used with any drive. So I created a 3D printable adapter and released it on Thingiverse!
Sonnet Adds ExpressCard Support to Thunderbolt—Equipped Macs
The Sonnet Echo ExpressCard/34 Thunderbolt Adapter demonstrates the power of Thunderbolt to bring flexible, high-performance connectivity to compact computers. But we are still in the first generation of devices like this, and it will be a while before prices drop out of the stratosphere.