Isn't that exactly what you're asking of Apple? Apple already has SMS. You want them to adopt RCS because it has cool new features that are lacking in SMS.
Let's say I propose this rule: Apple must publish the iMessage spec and allow other services to send/receive iMessages.
That doesn't force Apple or anyone else to implement any specific feature, beyond allowing others to send/receive messages. WhatsApp or Signal could decide they don't want to implement the iMessage protocol and they're free to do so. WhatsApp might support voice calling, but that doesn't force iMessage to implement voice calling. It's simply saying that third parties can choose to implement the iMessage protocol if they want.
There may be features that will only work within one platform, but that won't give anyone a lock-in advantage since others can implement those features if they're popular. For example, let's say Apple implements CoolNewFeature. They have to publish the spec for CoolNewFeature. Sure, maybe it will take 6 months for Google and WhatsApp to implement CoolNewFeature, but there's nothing preventing them from doing so. Likewise, WhatsApp already has voice calling, but you won't be able to do that with iMessage folks because Apple hasn't implemented that. That seems ok to me. If Apple starts to lose users to WhatsApp, they'll want to implement that interoperability. If it isn't an important feature, it isn't important whether they implement it or not.
To me, it seems like this is about preventing companies from creating walled gardens. It's not about forcing companies to adopt certain standards or features. Apple doesn't need to adopt RCS. If others could send/receive iMessage-protocol messages, it would provide an interoperable system. Some might complain that X protocol is better than Y protocol, but that's the history of everything. Ultimately, those types of things haven't prevented third parties from creating interoperability with less perfect protocols.
Just publishing the specs will not allow anyone to send/receive iMessages. It's built on a closed loop CA / certificate system.
Remember that Steve Jobs actually announced on-stage it would be an open protocol without actually discussing that with his engineers? The architecture is designed to be closed from the get-go, and opening up the iMessage ecosystem in it's current design is simply not possible without giving 3rd parties considerable access to Apple internals, affecting a ton of stuff beyond iMessage, and pose serious security risks.
Could Apple re-design a messaging system which would allow this and roll it out transparently to all it's users? Absolutely, but that would require a ton of engineering work, and won't be there tomorrow.
Yes, and that kind of anticompetitive behavior is what the EU is trying to curb.
