I am not sure if this is known already so decided to create a track.
If using this method of installation: https://tracker.pureos.net/w/installation_guide/encrypted_live_system_installation/ the system won't boot:
If using direct installer, the encrypted installation does work, I get nice graphical prompt to enter my encryption key password.
Not sure if this could be the problem with coreboot.
Device: Librem 13 v1, sata disk.
ISO version: 2017-08-12
Upstream issue: https://github.com/calamares/calamares/issues/772