I would like to connect a few (~4) Pi's together as part of an experiment. 3 of the Pi's will be connected to LORA modules and receive different serial data from various remote sensors. Each Pi will process and rationalise the data into a common format. The 4th Pi will receive the rationalised data and display it on a TFT.
Originally, I started by using standard RPI 3's and a LAN switch, however I would now like to use CM3 and a custom backplane.
I have searched as many threads as I could find on inter-CM3 communication without finding a clear solution to the problem. Then I found this thread viewtopic.php?t=162790#p1061380 on I2C slave mode using the BSC slave pins.
I've used I2C with 8051 a long time (27 years!!) ago to do something similar and was involved more recently (17 years!!) with CANbus. But I haven't been designing for many years, so rather rusty

I'm planning some tests this evening to see if I can make pigpio work between 2 RPI instead of a Pi and an Arduino. If that is successful, I will try with 3 and 4 Pi's.
However, I would like to hear of any other ideas or experience in this area, specifically:
1. Is it possible to get this kind of communication working or is it a complete non-starter?
2. Apart from bit-banging, are there any alternative techniques for (expandable) inter-CM3 communication?
3. Any other opinions or advice.
TIA!