Comment # 23 on bug 904987 from Joost W

Ok, some progress. I managed to boot into multiuser.target (not into
graphical.target) with 

- chrooting from dracut rescue shell into manually mounted system partition
(see above)
- changing system /etc/crypttab, using one line/entry with the
/dev/disk/by-uuid/ name of the encrypted partition, options "none none"
- mount /boot & dracut -f in the chroot

Now, the crypttab gets copied into the initrd and the password prompt appears
on next boot.

Though my boot is still not completely restored, as a boot into
graphical.target hangs indefinitely after "Switching root" at the end of the
systemd boot sequence, without X / SDDM coming up and without dropping to a
shell.
Work around for now is to boot into multi-user.target (add "3" to the kernel
boot command in GRUB), and then log in, afterwards run

systemctl isolate graphical.target.

Then X comes up. I have to 

systemctl restart NetworkManager

to get networking, then things seem to work ok.