Think that's exactly it, yes, this IS Ara only at the moment, but when they were asked this at the dev conference, there was much flirting of eyes and 'we're only doing THIS for now' comments.
But for phones, tablets, cameras, home security systems, media players, car units, plug in what you want, when you want. This concept isn't anything new in PC tech, with so many busses/drivers/external devices, it's known what's needed. This is a uber low power/hopefully incredibly flexible, driverless (to a point) something new.
Plug in that better camera, get the associated app to take benefit of the low light sensor.
Plug that smoke sensor into your wifi router for a cheap NEST like device. Have that wall mounted NEST AC unit near the door, plug in a bigger screen, attach the external camera to your doorbell (with fingerprint sensor? maybe versionIII), when someone calls, show the camera view on the NEST controller, and/or Chromecast it across to your TV.