To allow a full duplex disk system (e.g. a two disk system with RAID-1 for /
and swap (if needed for /srv and /home as well)) to boot from either disk, the
bootloader config must be installed at both disks. So when the one of the disks
breaks, the disk and bootloader redundancy make it possible to boot the system
even when the one the disk fails.

For the interested, it's like a bit as described in this article:
 
http://sysadmin.compxtreme.ro/how-to-migrate-a-single-disk-linux-system-to-software-raid1/

In the article reference above, the bootloader is installed on two disks as
follows:
grub2-mkconfig
grub-install /dev/sda
grub-install /dev/sdb

In YaST2/bootloader there is a disk section, but it does not seem to cover the
use case described above.
https://doc.opensuse.org/documentation/leap/reference/html/book.opensuse.reference/cha.grub2.html#sec.grub2.yast2.config.order

I think that it is an important use case for SLE as well (redundancy)...

Would it be possible to add such a functionality (e.g.) to YaST2/bootloader:
Install bootloader at:
[x] sda
[x] sdb
[x] when there are more disks