When we lost Hypnochan, we lost countless great pictures and manips with it. To prevent such a travesty from occurring again, we should make some sort of back-up, right? Is this possible/feasible?

Slayerduck said that he's gonna handle the backups sometime in the near-ish future. I'm more than content just to wait for that.

Also, one option if you have shell access, is to just backup the entire server.

This command creates a backup. It does not backup specific directories that aren't meaningful.

tar -zcvpf /tmp/fullbackup.tar.gz
--exclude=/mnt
--exclude=/proc
--exclude=/lost+found
--exclude=/dev
--exclude=/sys
--exclude=/tmp
/

(backup is stored in /tmp/ in this case)

And you can restore it with
cd /
tar -zxpvf fullbackup.tar.gz

You can also use this, it's open-source and has a GUI, plus it's very smart, unlike the above command which is rudimentary and doesn't handle differential backups.
backuppc.sourceforge.net/

Just saying this in case Slayerduck happens to be out of time to solve this in the mid term.