Where do you see this? In a conformal README or another README for this scala project? Because it is not necessary to derive the root private key to create a new public address. Instead, the next public key can be chained from the previous public key and the chaincode (seed). When pubkeys and addresses are created this way, the private keys are not immediately created, but are recovered the next time the wallet is unlocked. So while this is not an HD wallet (it's essentially the same as Armory's current file format, and there is no hierarchy), it does have some of the same deterministc address chaining properties.
I think I misunderstood your README: "Unencrypted wallets are unsupported and are never written to disk. This design decision has the consequence of generating new wallets on the fly impossible: a frontend is required to provide a wallet encryption passphrase."
Where do you see this? In a conformal README or another README for this scala project? Because it is not necessary to derive the root private key to create a new public address. Instead, the next public key can be chained from the previous public key and the chaincode (seed). When pubkeys and addresses are created this way, the private keys are not immediately created, but are recovered the next time the wallet is unlocked. So while this is not an HD wallet (it's essentially the same as Armory's current file format, and there is no hierarchy), it does have some of the same deterministc address chaining properties.
The code for performing this pubkey chaining can be found here: https://github.com/conformal/btcwallet/blob/8795534408b47685....