Ohh fancy! No I didn't consider radar, watching that video now.
The main consideration for the motion sensor is power consumption -- Photon's PIR consumes ~2µA. Any idea what the power consumption is for these radar sensors?
Speiss’ videos are good about measuring current. He was an early one on the coin operated ESP8266 movement. Looks like they are outside your energy budget: 2.3mA is the lowest.
The video I linked was from 7 years ago? Here is a more recent one but it doesn’t seem like he measured energy consumption: https://youtu.be/s-GzUTyIH9c
You'd get a design identity ++ if the dovetail backplate was more similar to ejecting toast. . . .but looks like that isn't in the final anyway.
Did you consider radar[0] instead of PIR with the MPS430?
0/ https://www.youtube.com/watch?v=9WiJJgIi3W0