> could it be used as an encrypted chat
Yes, any communication tool and any cloud service CAN be used to pass encrypted messages. After all:
The cat ate the grapes. What does that mean? Nobody knows without the key.
And besides, 8911 54dd 25d25 eb7a 0fae e16.
It's trivially easy to send encrypted messages using any platform or protocol that posts / sends whatever you type / paste.
> Will password managers like Lastpass or or self hosted ones like Bit Warden or Vault be the next place for criminals to communicate
No. They are particularly ill-suited for that purpose.
They would be a poor choice both in terms of practical use and also security. They are a poor choice simply because it's not a messaging platform. There's no contact list or anything. There's no notification that you received a new "message", etc.
They are also particularly poor for security, because to either read or update the password (message), you need to have THE master key/password. You'd have to share the master password with whomever you're communicating with! That makes the entire idea mostly useless. That's like sending an email with a password protected zip file and saying "unzip this file using the password "Kaboom". Well that's pointless, because anyone who sees the message has the password.
Encrypted messaging apps such as Whatsapp and Signal don't have *A* key for the conversation, used to encrypt and decrypt it. They have a total of FOUR keys. When I send you a Whatsapp message, I use your public key. The essential thing to understand here is that the public key, which I use to encrypt the message, can NOT be used to decrypt it! That means I can send you an encrypted message, without including the decryption key in the message.
You send me your public encryption key, and keep your decryption key private. That's how Whatsapp provides secure messaging, while LastPass doesn't. Lastpass and other password managers are secure only for sending messages to yourself, where you don't have to communicate the master password to someone else.