In my limited experience with BizTalk it seems that BizTalk projects and Visual Studio version are somewhat locked to each other. For example, you can\'t open a BizTalk 2010
As of today (Nov 5, 2013) it does not. It appears that there is a 6 month lag between releases, so we can expect it to be supported in several months. For now, you'll have to stick to 2010 or 2012.
Source: http://blogs.msdn.com/b/biztalknotes/archive/2013/10/29/biztalk-2013-compatibility-with-latest-platforms-of-microsoft.aspx