This proposal is not for the faint of heart.
Most of us have passwords of varying levels of security. At the lowest level we have passwords for “throw-away” free accounts whose security we barely care about. At the highest level we might store, for example, cryptocurrency keys or passwords for other password managers. And there are passwords at various levels of security in-between.
The feature request here is to support nested vaults. Your password as before unlocks your main vault. But within this vault you can have other vaults, each with its own password. And once you implement a vault-within-a-vault, it should be easy to extend that to N levels of nested vaults, N being limited only by available computing resources.
At each nested level, yet another password is required to unlock that level.
Passwords that need a high level of security might be stored in a vault that is three or four levels down. To access that vault, you would need to unlock each containing vault first.
The general idea that I am proposing is ancient. it used to be called a “ring system” in operating systems, in which you had nested rings, and the deeper you went the more privileges you had. The idea of security levels is also implemented in classifications such as Confidential, Secret, and Top Secret.
In normal operation, the user would enter his normal Bitwarden key. This would unlock everything in the main vault. These would be all the low-security passwords only. The user can unlock a high-security nested vault as needed, making more higher-security passwords available, but still keeping the highest-security passwords inaccessible. Only rarely would the user need to unlock more deeply nested vaults. And the user might choose to unlock higher-security vaults only on a very secure machine.
So you could safely use your password manager while in a coffee house, keeping only the main vault unlocked and only the less secret entries possibly-exposed if somebody snatched your laptop from you.
Likewise, while crossing international borders, you could unlock the main vault under duress, while being unable to unlock nested vaults because you would not have the higher-security vault passwords with you when traveling.
Each nested vault would preferably have its own timeout, and most users would set the timeout shorter for higher-security vaults.
Searches would presumably only work on unlocked vaults.