Sadly, no word yet on when Season 2 will hit U.S. shelves, but I hope soon since BBCA has aired the Series 4/Season 2 finale.
It won't surprise you that I've been checking Target's website periodically. XD Not gonna fall for THAT again!
How the BBC America pick-up will affect NBCU's decision to release it and when is a mystery to me. I would certainly hope it arrives before the fall when Series 5 airs. (And hopefully Series 5 will air here the same time as the UK.)
Also, I'm curious to know what the Series 4 extras will be - I distinctly remember Emilia tweeting about recording an episode commentary, but she didn't turn up on the Series 3 release!