Is Left 4 Dead 3 Being Built On A New Engine ?

Alright, Valve and L4D fans, prepare to take this news with a grain of salt as nothing is confirmed of yet. Apparently, a new image has been surfacing around the internet, said to be from the computer of a Valve employee, which was taken during a tour by some fans. Now if you peek closely at the image we have attached below (be sure to click on it for the full resolution), you can see repeated mention of a Source Engine 2 and a line for Left 4 Dead 3. Now, obviously a lot of speculation is going on that the new Left 4 Dead game might actually be in development on a new in-house engine, which seems to be a followup to the highly acclaimed Source Engine.

Now what I am most interested in knowing is, where will the three-quel take place? Will it feature brand new characters, and will it have exotic and powerful new weapons? For now, only time will tell, because as of now, Valve is not commenting on any speculations or rumors, in line with their company policies. So again, take this news with a grain of salt, and keep your fingers crossed. Lastly, stay tuned as we will keep you updated on this situation!