> What if one day Signal, Telegram or WhatsApp want to implement something "different" that could make messaging better but this policy is making things harder to implement because it would be impossible to make it interoperate with other messaging apps?

That's still possible. The company owning that platform just has to ensure that its services are accessible by any client. Protocols/APIs can still be further developed or brand new ones introduced. But they still have to be documented & be made accessible.