Well this sure came out of left field. Capcom and Valve have apparently teamed up for some cross over content in which character from Left 4 Dead 2
will appear in the PC version of Resident Evil
6 and enemies from Resident Evil 6
will appear in Left 4 Dead 2.
Courtesy of Kotaku
apparently they got this notice in their inbox today and its also been confirmed via Famitsu
although that link is all in Japanese. Best of all it appears this content will be free for everyone!
Capcom and Valve are pleased to announce the Resident Evil® 6 x Left 4 Dead 2 project. This crossover project between two of the interactive entertainment industry's most respected publishers will see characters from Left 4 Dead™ 2 featured exclusively in the forthcoming PC version of Resident Evil® 6, while enemies from Resident Evil 6 will invade the PC version of Left 4 Dead 2. All content will be made available completely free for fans of either game to access and play.
As someone that is a huge Resident Evil and Left 4 Dead 2 player I am really excited about this.
More info as it becomes available.