Great to see this work being talked about. I work on the media signal processing team at Google. My team built this beamformer before I started, but I'm happy to see it being used in PulseAudio. The paper hasn't been released, but the nonlinear beamformer code is open source. You can find it in WebRTC.
https://chromium.googlesource.com/external/webrtc/+/master/w...