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.

[–] miss_brainfart@lemmy.ml 4 points 11 months ago

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.