I just found out about this project after reading the news about the troubles with passive radar source code. What a cool project and an awesome looking board! I will definitely order one of these.
I have one question, or maybe it is more of a feature request. From what I understand, you guys automate the aligning of samples from multiple rtl-sdrs. I wonder if you could also add support for a 1 PPS GPS synchronization signal too? There are inexpensive GPSDOs out there, which provide a 1 PPS and a 10 MHz output. The 10 MHz could be used to generate the master clock, and the 1 PPS could be used to provide absolute timing.
There are many ways to accomplish this. For example, injecting a GPS 1 PPS gated noise pulse into the receiver. As all channels are already aligned, one would only need to do this on one channel. One could possibly even consider estimating the absolute frequency of the master clock using the 1 PPS signal if generating a master clock from the 10 MHz is too expensive. A global timing reference would allow triangulation based on time of flight with a network of receivers sharing snippets of complex voltage.