Cool! That design makes sense to me.
Do you anticipate other wallets besides Vessel will be able to use the hardware wallet? Hive Keychain support would be convenient.
Posting/memo key maybe safe to be in a password manager like Lastpass.
Nice. BTW I've switched from Lastpass to Bitwarden. Bitwarden is open source and has a nicer interface and design.
Yeah there are already javascript libraries to interact with ledger so I am sure Keychain and others could adapt when it is working.