A recent domain registration has led to a surprising discovery. XboxEvent.com has been picked up by a division of Rapid Systems named U.S. Techs, the organizers of Microsoft's E3 events. While the site has yet to be updated, if Microsoft was to... say... plan an event, this would be a good place to announce such a thing.
The obvious leap to make is that this is one of the early steps Microsoft is taking to announce their next Xbox. Considering Sony called their event the PlayStation Meeting 2013, Microsoft can call their meeting the Xbox Event 2013! It's stupid and also perfect.
Beyond that, there's really not much else to say. Conversation at the PlayStation event made it sound like folk are expecting a Microsoft announcement in late April. I wouldn't expect a teaser for the public for at least another few weeks, maybe longer. Maybe even months if folk at the PlayStation event were wrong.
It looks like a new Xbox is certainly in the works.