What I meant by building it on top of DMs mainly refers to the encryption/decryption protocol, not the DM feature itself.
Any encrypted content requires both the sender and the receiver to use the same protocol. Jumble plans to use NIP-4e to encrypt gift wrap events. At the moment, other clients don’t support this protocol, so even if I implement this feature, it may only allow private replies between a small group of users.
These replies would still appear in the comment section like normal comments, but they would only be visible to the intended participants.