The name is Whitebox as opposed to blackbox because everything about it is known. The more you know the more you can do with it! The source code, schematics and board layouts are on github. Unless you have looked into SDR programming, there may not be much useful there. If you have looked at gnu radio or any of the RTL-SDR programs, this should look quite similar.
The project hasn't changed status in a little over a year, although the author has done several recent interviews on some ham radio podcasts. There was quite a bit of discussion around the 2013 Dayton Hamvention. I believe this device is pretty solid, but I don't have one yet.
Remember that UAT frequency is 978MHz, toward the top end of the limit if this device. It should be no trouble to write the code for a UAT device. The USB out from this board could easily be connected to an external computer, including a tablet.
It will take some software development to finish this project, but with a little bit of work, suddenly there would be a UAT available for under $1000.
Flying Magazine recently published an article about a portable ADS/B in/out device that is under $1500. It may not be under $1000, but it has a chance to be a popular device. The SkyGuart TWX is a portable device that listens on both 1090 and 978MHz and transmits on the 978MHz. It also has GPS receiver and WiFi for connecting to a tablet.
Are we getting close yet?