Okay, I just bricked my device again. Bash required the library libc.so.6, which in the Kobo is just a symlink to libc-2.11.1.so
Without realizing it, I deleted the symlink and just replaced it with the actual library, and the device died.
I have found a static version of bash, though, so after restoring the SD I will try this:
https://github.com/robxu9/bash-static