Yeah.
In extreme cases, Keychat can achieve the following:
changing the encryption key for each message,
changing the sending address for each message,
changing the receiving address for each message,
changing the sending relay for each message,
changing the receiving relay for each message.
You should make that the usual case not the extreme. Will Key Chat control a server as well or will it operate only with third party servers?
Users can choose which Nostr relay to use, as long as the relay supports NIP-4. 
Why NIP-04? That has been fully deprecated right now. Please don't use it.
This should be a legacy issue because kind 4 was the earliest DM solution, and most clients and relays support it. We can change it later.
Additionally, we believe NIP-4 is the simplest and should not be discarded outright. It can complement other NIPs.
NIP-04 is not secure. I don't see any point on releasing something with a complicated double ratchet mechanism using that rudimentary/faulty encryption scheme.
