2K Australia, the developer working on the Xcom reboot, is helping Irrational Games out on Bioshock Infinite. The studio also helped to put the finishing touches on the original Bioshock, so this doesn't come as a surprise. This puts some perspective on Xcom's recent delay into fiscal 2012, which runs until March 2013. Bioshock Infinite is a flagpole release for publisher 2K, so it's likely they'll want the game polished and finished post-haste.
We still haven't got an official release date for Bioshock Infinite other than a wide calendar 2012 window. With production ramping up to include a second team, it seems likely it will be out in the first half of 2012. At least it doesn't hurt to hope.
Bioshock Infinite looks like a 'spiritual' sequel to Bioshock, chronologically taking place before the original game. Whether they take place within the same universe has not been confirmed nor denied. The game turned heads with a gameplay demo shown at E3 2011 and anticipation has been building ever since.