The plugin would allow a roomba to be added as device in the indigo interface. This would require the roomba to have a rootooth or equivalent device and it would pair with the Mac as a bluetooth serial device.
From there the user would be able to manually control the roomba from within indigo, see it's current status, send it off on a cleaning mission or ask it to return.
I personally don't have any interest in manual control just the ability to send it on a mission or ask it to return. I would also generate statistics such as "last mission completed at 9:25 am, it took 25 minutes".
This sort of functionality currently exists as stand along programs on the Mac. http://hackingroomba.com/code/roombacomm/