Yeah, I've also had difficulty finding something with enough I2S. It was a while back and I've used Sprocket carrier for Jetson TX2 - it had 6 lanes, so up to 96. It was for a SODAR application, so the sampling frequency was not that critical and to me it felt like the perfect trick to make an array with off-the-shelf hardware. So I was just curious, if this was something you've considered.
For something indoors, yes, I can see how low sampling frequency gets very limiting. And 192 microphones, that's really pushing it. Love it.
The $2/mic vs $0.5/mic argument is a fun one. You've obviously poured enormous amount of engineering in there, involving PCB design, FPGA and network programming, writing custom CUDA kernels, signal processing, PyTorch, the list goes on. And you've had 4090 plugged in your PC in 2023. Classic hobbit in a mithril vest ;)