The power imbalance when a semi-monopolist joins an open protocol is a really hard problem to solve.

Google all but killed XMPP by using it in GTalk/GChat/Gmail/whatever it's called now. They probably had no ill intent from the beginning, but their very presence gave everyone the need to quickly be if not bug- then quirk-compatible.

By the time everyone came around they suddenly de-federated everyone and with vague references to spam, which everyone knew was bunk. But the damage was done.