I'll admit not really played with it yet... as I need to finish off another project first... so might be a week or two yet
but... what i understand is, the FPGA runs firmware which you can program using icestorm, and what they have then is an SPI interface between the arduino and the onboard ice40.
so you have a means to communicate between the two parts,
they are currently showing uploading new firmware to the ice40, and communicating with the matrix, but I assume you can do whatever you want over the spi.
cool @killor looks interesting... will look at their site, and also icestudo ida
(gonna need all the help/info i can get )
the doppler is also completely open source (hardware and software).
it be great if perhaps the two 'teams' could foster some kind of synergy...
anyway, as I said not explored it yet - but looking forward to it.