There’s a new (May 2014) BizTalk Server 2013 R2 Licensing Datasheet and FAQ. There are no changes to the licensing, but the updated datasheet adds in the Developer edition, has a (quite useful) table to compare editions, and includes a new FAQ right at the end which details the licensing limitations of BizTalk Branch edition.
Get it here: http://bit.ly/UR1LBt.