Interoperability is a weird one though. Imagine WhatsApp can connect to Signal, and people use this feature. What would then be the point of using Signal, if WhatsApp gets the data after all?
(Signal has already announced not wanting to support this, I just used it as an example)
As I understand it, your example should be the other way around. WhatsApp will need to offer a public API to allow Signal to send and receive messages to/from WhatsApp users.
Signal is unlikely to be deemed a gatekeeper, so can keep their closed communication ecosystem. They can just optionally choose to support interop with WhatsApp. If they prefer, they can also have big warning signs in the UI, when their users decide to utilize that interop.
Whatever way it works, I could see people giving up certain services if they allow interoperability with the gatekeepers, because why use these alternatives then.
But then again, the services that take privacy seriously won't do it in the first place, so it should be a non-issue.
Since WhatsApp is proprietary, we don't know if the users are the only ones who can decrypt their messages. I'll always have to assume Meta can read everything, which is the most sensible data they could possibly collect.
So that alone should be reason enough to avoid it.
Yes. I don't endorse WhatsApp. What I meant is if you chat with 15 people out of which 5 use WhatsApp, only those 5 chats are potentially readable by Meta. Because those are the only chats which will get sent to Meta servers.
So you have the benefit that the other 10 chats are not readable by Meta.
At this point I just assume Meta, Google and Apple have my number due to people storing the number on their devices. Amazon also might have it because people might have paid me via Amazon Pay (and given it access to contacts).
I saw the technical discussions (if you are a tech person I would recommend watching those on YT) and it seems that EU is trying to find some middle ground where companies won't have to incur a lot of losses but still be open and create a fair environment for newcomers.