Other than a basic understanding of what it is, I don't know anything about XMPP. What's wrong with it? Or, more specifically, what does it do poorly that other things have eclipsed?
It is federated in such a way that it is sometimes difficult to establish new features, as there are a multitude of servers and clients, which would all have to support said new features for them to stick.
Some see that as an advantage, but it definitely doesn’t help ‘innovate’ and re-invent the wheel every other month. GPG encryption, for example, while standardised in XEP-something, is still not really supported in widely available clients. OTR encryption is more of a layer atop the actual protocol and hence somewhat inelegant (and also not that widely available).
Also it’s XML-based, which could be argued is even worse than base64, but that should be a rather small concern given how popular JSON and the likes are nowadays.
But Google, as a wealthy company and the controller of such a big chunk of the XMPP user base, was (maybe uniquely) in a good position to overcome these problems. It could have established a de facto standard set of supported features, and maybe pushed out some code to help clients implement awkward bits of it.
