Read-only file system for NanoPi
Instead of a UPS, we can explore a read-only file system (or more specifically a Unionized file system as described here http://www.logicsupply.com/explore/io-hub/how-to-build-a-read-only-linux-system/) and take advantage of the 2nd SD card spot on the NanoPi.
Corruption may still occasionally occur on hard shutdowns, but only logfiles will get corrupted - the system will still boot and run just as well as normal
A few years ago someone did this with their Rpi: https://www.raspberrypi.org/forums/viewtopic.php?f=29&t=23154