12 words seedphrase is the way.
Amber already implemented it btw. 
Discussion
Only works for new accounts. You need to start from scratch if you want to use seeds as predicted by NIP06
Why is this?
Nip06 is based on the Bitcoin seeds. The main point of bitcoins version is to make it impossible to figure out the seeds from any of the private keys related to a UTXO.
But we could still just create bip32 seed words from a single private key to use for a backup/restore, just can't derive the existing key as part of an HD set?
