Here's a little insider tip for you. Head to this cool, underground website called Twitter.com. Find a user called @XboxP3. Click the "Tweets and Replies" tab. Congratulations, you now have access to all Xbox-related news before it's official!
Phil Spencer loves engaging with his fans (and occasionally, his detractors), and that leads to some exciting, presumably achingly pre-planned responses. Take this tweet (as reported by VG 24/7), made in response to an innocent, now-deleted enquiry:
@Masih3KA We should have new exclusive IP at E3. I'm trying to make this E3 more about 1st party than past E3s.April 19, 2015
Just like that, we have a new reason to look forward to the Microsoft press conference. I'm not a huge fan of that "should" in there - I want certainty, dammit - and obviously that "new" part rules out any real speculation as to what the new IP could be.
Of course, there's a chance it could be another Ken Lobb-sanctioned reboot of a dormant franchise, a la Killer Instinct, Crackdown and the (probably dead) Phantom Dust. You can also hang your hat on the fact of it being playable on both Xbox One and PC via the new Windows 10 integration.
I would say to watch this space for more but, instead, let's all just go and watch Phil talk to people, eh?