Lockheed is pushing this technology on the basis of security - you can plug this into any computer and basically use the keyboard and screen while bypassing its innards - and the datastick computer comes with its own mil-spec security.
I'm seeing a whole bunch of other possibilities though - like giving full computer capabilities to the hundreds of millions of people in the developing world with a mobile phone but not a PC - all you need is a WiFi or Bluetooth connector.
It’s not a new concept; they’ve done it for years with PCMCIA devices that handle sophisticated cryptographic tasks that people don’t want running on the OS of networked computers. But PCMCIA hasn’t been ubiquitous for a while so moving to USB makes sense.