Thanks you for sharing this journey into ultra low power. Using a LiPo battery (which could be quite a bit bigger energy storage wise than the CR2032) do you think it would be possible to do the same or is it a binary choice with using 3V3 as Vin or the Li+?
I have been working on a more sophisticated presence detection using an AMG8833 - LR-TAS - the Xenon allows some fairly sophisticated feature extraction and scene activity detection. The downside is the processing time and power! Next step is to sleep/stop as much as possible - the sensor has a nice feature whereby it can periodically read the thermopiles and then generate an interrupt if any have detect a temperature over a threshold.
I am guessing that a X-SOM when/if it arrives would allow much better power control since the power management circuitry is not on the SOM.
On the PIR side of the equation had you considered using a low power MCU to do the digital signal processing and then wake the Xenon for a bit mesh comms when it has detected some movement. I am guessing the analog signal path does some difference to create a detect signal to the Xenon?