Let's place bets on the name...

  • Xbox 720 - not particularly original. I didn't like the original "Xbox 360" name anyway.
  • Nextbox - Internally at Microsoft we use "Next" as a placeholder name making this unlikely, plus it's going to get confusing when the 4th generation Xbox comes out.
  • Xbox {meaninglessName} - Nintendo did this with the "Wii U", Sony did it with the "PSP Vita", and we did it ourselves with Windows Vista and Windows XP. Word inside the company is that we, as an organization, have abandoned silly marketing gimmicks and are being more straightforward... if simple.
  • Xbox 3 - see above, it's simple and direct, however remember one reason we didn't name it the "Xbox 2" was in order to look better compared to the PlayStation 3 ("Xbox 2 or PlayStation 3 vs Xbox 360 or PlayStation 3").
  • Xbox S - Something that Apple and Samsung are up to (and car manufacturers) - take a brand and add "S" to the end - for sport, speed, or some other connotation you fancy. However we can't use this because we just called the revised Xbox 360 the "Xbox 360S".
  • Xbox - reboots are a thing nowadays - Batman, Superman, Wolfenstein, Tomb Raider - it stands to reason they'll just call it "Xbox" with no qualifier. If the rumors of total backwards-compatibility are true (because it's an x64 chip that'll be able to run the old Xbox's x86 code fine) then this works even better, because the new Xbox can play the old Xbox games without any issues, thus actually reducing customer confusion.
  • Xenon - this is the name of the chipset. It's possible, but unlikely they would use it as the name of the console.

My money's on either just "Xbox", or "Xbox 3".