No, not exactly. WebRTC has no concept of interoperability between services, only between clients. You need a signalling server to communicate the initial call between clients, and if you wish to connect clients across services, then those two services would need to connect to each other in some way, which is not detailed in the spec.

There are efforts to use SIP and XMPP for this, but that only solves the WebRTC-part. If you want SIP-clients to interconnect, you need expensive hardware/software to transcode the streams, and you loose the P2P-part. WebRTC is not a golden cow of interoperability between services.

No. It just makes it easier to build even more services that can't talk to each other. What we need are federated services, like email and XMPP.