first of all: thank you for creating Duplicati, the backup software that matches my needs exactly. After having had quite a hacky approach to backups with several butchered scripts that barely do the job, I recently stumbled across Duplicati and all I can say is that I am very impressed by its feature set and ease of use.
I like to print my configuration to store it in a non-digital way. A minor neat feature would be to show the passphrase (additionally) as QR-code. I know, creating good software is all about focusing on the right features, but I can imagine this to be useful.
I thought about it this way: currently I set up some backups with long and strong passwords and print the configuration. With a QR code on that page it might one day save me from the hassle of telling capital i’s from lowercase L’s and pipes, and 0’s from O’s and so on.
Export in armored (ascii) format and run qrencode iirc. That is available on Ubuntu (don’t remember if it was installed by default or if I had to install it manually). I would never trust a Web provider to encode private keys.