Thank for your kindness :)
Fun fact: It is in fact a bip32 master key. But you can only put funds on it if you know thy tools.
You developed a tool and without any doubt have more experience in the field and thought a lot about the best approach, so I'm really interested in you opinion.
I played with https://lnpass.github.io, from the export function I grasped what you mean! You would like to create a "closed" login app where the bip32 master key is not so obvious, so it cannot be used as a standard wallet. Fair, but I would prefer a more transparent approach where the user can easily export and migrate to to another LN wallet, for example.