Privacy and interoperability are mutually exclusive. A high level of privacy (for example hiding metadata on private messages) requires a high level of technical sophistication (for example SimpleX or MLS). A high level of interoperability (apps must be reasonably easy to build) requires a low level of technical sophistication (json, websockets, simple network topology).
Discussion
trade-offs!
all apps don't need be privacy apps
I think that Gift Wrapped DM or other 'hacky' methods to improve DM privacy is good enough for initial conversations between users. Better than NIP-04 default DM.
If the users want to continue their conversations in more private settings then they can exchange their contact (SimpleX contact) via Gift Wrapped DM and continue their conversations on SimpleX
Not mutually exclusive, but they tend to exponentially damage each other, especially at the extremes of each axis. Very interoperable systems are more affected by smaller variations in the privacy spectrum than less interoperable systems and vice versa.
I don't think they are mutually exclusive. It's just that a good solution for both at the same time is orders of magnitude harder to find than a medium solution for both.