Storage of Private Key Data?

[Kefkius]

Eventually, a tool will exist that can make use of private keys. (Transaction Builder really already fits this criterion, as it could have the ability to sign transactions.)

The question of how to deal with private keys presents itself. Since Hashmal is intended to help developers, it makes sense that someone who knows what they're doing should be unencumbered by measures designed to protect less-experienced users.

Nevertheless, I think it's unwise to go beyond storing private keys in RAM (e.g. writing them in the config file). Doing so would require something like:

1. Creating a system of optional key encryption, in which encrypted keys are stored and the user must do something to decrypt them when they're needed.
2. Something else?

Is there a feasible use-case (e.g. tool) in which permanent storage of private key data is necessary?

And if so, is there a better way to save private key data than the option listed above?