mkinitfs does not support unlocking multiple crypt devices
When having encrypted root on btrfs raid1, you need to unlock multiple block devices and there is currently no way to do so.
I've added support to do it and sent it to ~alpine/aports ( https://lists.alpinelinux.org/~alpine/aports/patches/3068 ), but I'm also creating this ticket in hopes to get some feedback on it.