I had no idea such a thing existed. http://www.gocontrol.com/detail.php?productId=6
Maybe I was naive, but the lack of a plug in Zigbee radio always struck me as one of the big stumbling blocks for adding Zigbee support to Indigo. To use my own example as an illustration, the lack of Zigbee support in Indigo was the #1 reason I didn't make the switch to it sooner from SmartThings. This is because I had a handful of Zigbee sensors that were going to become useless the moment I switched.
Of course in the long run I'm much happier and don't begrudge the 2 or 3 door sensors and the keypad I have in a drawer now. But I'm sure there are people out there looking for another solution and who have a couple hundred dollars invested in Zigbee sensors: SmartThings users, Iris users, that crowd.
So this isn't really a feature request, more of a "hey, look at that. I'm not going to use it now, though I would have two years ago. It might offer a way into new markets."