I guess the fundamental big problem you are facing is SD card corruption. In our experience, we've found the SanDisk Extreme Pro cards to be most reliable. (coupled with a good power supply).
Read-only rootfs is almost a must have for any production environment.
resinOS does not satisfy all your requirements (nfs boot, state in memory etc).. But we do have stuff in place to reduce the problems you are facing.
- There is an initramfs in the kernel. When the kernel loads in memory, it runs fsck on the root/data partitions before mounting the rootfs. - The rootfs is read-only with only a few configuration files in the state partition. - Applications run inside a container so you can basically run rasbian on top of resinOS.
I wrote more about resinOS in another comment highlighting remote application container updates/vpn access etc.
https://news.ycombinator.com/item?id=18093336
Disclaimer: I work at resin in the OS team. I've noted down your feedback about running purely in memory.