It's above my head, but there are a few PRs in the NIPs about this: https://github.com/nostr-protocol/nips/pull/574
Discussion
Just read it. Looks like a good direction. One question I have is, before 44 is merged, can we have a compatible way of doing kind4 that leaks less metadata. For example, put timestamp in the encrypted content as well.
Some would say leaking metadata is a feature, not a bug
I thought they were just joking or trolling. It could be a good tool to spy on your partner to see if they are cheating for sure. That's like the first "useful" thing came up in my mind.
If the metadata leakage was surfaced in the user interface, it wouldn't feel so sneaky. IOW, it could be like a game, "check it out, I publicly DM'd Jack and he DM'd me back". Obviously, there should be a fully private solution, but for 90% of use cases, the leakage is fine, and could be kind of fun.