First of all, I want to say as someone who places devices in remote places, I can totally understand how frustrating it is to have them go off-line and require a manual intervention. I have been working with the Particle platform for a few years now and have felt some of the pain you are referencing with deviceOS updates.
That said, I do think you can have a stable platform with this product and I think you will find that folks are ready to pitch in and help you in this effort. As you called out the work I am doing on the carrier board, I wanted to provide an update. I have been delayed in updating this work because of some of the deviceOS issues around sleep, the new power configuration API and PMIC lock-ups. However, I am convinced that these issues have been resolved or have reasonable workarounds. Therefore, I went ahead and placed an order for the 3rd Generation Carrier Boards and they will be delivered from MacroFab today. I was going to test them and update the carrier board thread to close out that effort as complete.
If you are interested, please send me a dm and I can sell you a board for testing. Once I field these for a month or so, I plan to place a larger order and will invite folks to pile on. I do not make money on hardware but if more people order together, the price goes down for everyone.
My carrier board does have a hardware based watchdog and my intent is to continue to improve this over time through watchdog firmware updates. I can say that I have devices that have worked reliably for years and my hardware and software is open source so you are welcome to any of it that is helpful.
Thanks,
Chip