BIP85 lets you create child seeds that derive from a common parent, but what's the benefit? To leverage existing backups? How do you restore child seeds if you lose them? Can you list/obtain all children from the parent?
Discussion
Yes. Once you have backed up your parent seed and passphrase, any following child seed you generate doesn't need to be backed up. All you need to backup is the index number of the child and whether it's a 12 or 24 word phrase.
If you ever need to access a child you can simply use your parent seed backup and entering the correct index number will give you your child mnemonic.
It's far better than having dozens of mnemonic seed backups
Plus, if any child's are compromised it doesn't affect the parent in any way.
I see, so you only need to backup the metadata (index, seed length) for each child metadata.
I wonder if it's cryptographically possible for wallets to search index 0-100 and list them automatically, eliminating this requirement.
That would be extremely powerful, covering 99% of usecases with zero backups of child data.