L4D3 Leak or Just L4D2 Port?

NeoGAF user crazy buttocks on a train has come across what they claim is a confidential presentation from Valve showing images of Left 4 Dead 2 rebuilt in a new Source 2 engine. This long rumored new engine could be the basis for L4D3, so the internet has collectively worked itself into a frenzy of LFD3 rumors. Don't get too excited; we all know Valve can't count to three.