While Microsoft has yet to comment, unnamed sources have pegged the Xbox 720 release in time for the holiday shopping season in 2013. This information has been mirrored by many gaming sites and players, as it makes the most sense in both time period in year and month. The current generation of consoles have hit a wall, and they cannot be pushed any further with the hardware we have now. A new system is due, and we should hear about it soon.
That "soon" might not be E3 (Electronic Entertainment Expo). The source says that Microsoft is debating whether an E3 announcement or a separate venue geared solely towards the Xbox 720 would be more appropriate to build hype for the new console.