A lot of people here recommend using simplex for private messaging and there is hope that someone will develop a standard protocol to integrate simplex into nostr clients and that clients all jump for that.

In fact, if you look at the original spec for how DMs are handled, it says at the top that it shouldn't be used. https://github.com/nostr-protocol/nips/blob/master/04.md

We're in a traditionary period, especially because developers are always scared of breaking anything that users may be using, even if that thing is not recommended to use.

Often there needs to be a migration plan before developers consider dropping a feature.