Valve Time, a somewhat credible fan site, has just found files for Source 2 in the Source Filmaker.
Here's a direct quote from Source Filmaker's script files:
'''Return an str with the current engine version.
If key doesn't doesn't exist, assume 'Source', otherwise invalid -- assume next-gen 'Source 2'
Quote from Valve's site under the "About Valve" section:
"We donít like to brag, but Source is considered the most flexible, comprehensive, and powerful game development environment out there. And itís about to get even better."
Some dev tool icons for Source 2 were also found:
You know you're pumped. You know what this means. I find it incredibly hard to believe that Valve would not create/release Half-Life 3 for Source 2 considering that GoldSource was released with Half-Life and Source was released with Half-Life 2. Maybe we'll see some non-valve Source 2 games around its release too. Vampire: The Masquerade Bloodlines 2 anyone?