@Gargron @mosseri One-way? I.e. you can read, but not interact?

Many commercial platforms that had access to open protocols were one-way and stayed one-way. The idea is to suck people in who use the open protocol, and not give back.

I remember the times where all important chat platforms from Google Talk to QQ were XMPP, and you could use essentially any XMPP client to talk to them, BUT they never did the interconnection with other XMPP servers.