I don't see it.
How does this integrate with Steem's accounts and how do you foresee other steem app inter-operating with this?
I already have about 10 private messaging app and the biggest problem with them is segmentation, I like Signal Messenger because it's easy to set anyone up (no login:password to remember) and it also integrate as my SMS app.
Why you upvoted your own comment?
You want to negative vote others and doing self voting your own contents.
Double standards
Encryption and decryption of the messages are done with Steem account (memo key) and messages are stored off-chain on eSteem backend for the reason I have briefly talked in post. Since all messages are encrypted (nobody knows content of the message) we can provide API and sample scripts for any other apps to use if they choose to integrate it. Unfortunately, it is not replacement to any other messaging apps that has their own users(base). But for now why postpone feature if we can implement it with what we have/can. Later if we will have pruning functionality, storing messages on Steem blockchain would make more sense and can easily be adopted by eSteem and other apps.
Are you going to encrypt the fact of sending a message? In other words, if Alice sends a message to Bob a third-party will not be able to decrypt the content of the message, but the fact that Alice is writing something to Bob will be publicly available to everyone, is that correct?
If we make API public yes, otherwise it stays on eSteem servers for 7 days before erased. Note that it is off-chain and if it was on-chain that would be traceable unless we have stealth transactions.