WebRTC let's you build server less web apps.
It's like you'll also need DNS, which isn't decentralized either.
If someone wanted to write this as a WebRTC-based decentralised version there is nothing stopping them using something the like the public signalling servers that Mozilla uses for their Hello service.
Also, if some users wanted to run a signalling server themselves, that's ok too.
You're right, there are public signalling servers and such. I just wish we weren't so restricted in setting up direct connections, such that you could do it through your bootstrapping peer in the network.
But at the same time, if someone wants to try: yes, it needs to be browser based, and the lack of a server doesn't need to be a limiting factor anymore.