Payday + Left 4 Dead = ?

Payday: The Heist developers Overkill Software, have teased an upcoming collaboration with Valve that seemingly mixes elements of Payday: The Heist with elements of Left 4 Dead.

"As perceptive gamers will have noticed, several hints have recently been dropped into PAYDAY The Heist, which has led to various rumors. We are excited to be able to confirm that an in-depth collaboration between OVERKILL and Valve is currently in production.

We are working on a very cool blend of PAYDAY and Left 4 Dead. I am sure it is so exciting that it will have some players check into the hospital before we are done."

So what could it be? A full game sounds like a stretch, but perhaps we will see some kind of zombie infested level released for Payday: The Heist or reversely scenario with robbers for Left 4 Dead 2. The former sounds like the most likely option. Regardless we are very interested in learning more.