I've never heard of this, it's interesting that someone in Valve would decide to say that, when as far as I know, they haven't even verified that they're currently working on any half-life game (I might have missed that as well though :p). do you remember when/where this was?
Also, he said...
except, unlike the other titles you mentioned, episode 3 won't be the third installment in its series but the fifth (HL, HL2, HL2:EP1, HL2:EP2). Even if you looked at it starting from Half Life 2 - it's still the fourth game.
The only way your pattern makes sense is if we're talking about a...
I'm actually pretty sure it didn't.
The thing that bothered me the most was the voice acting... Obviously this is a non-profit thing, so they won't have big Hollywood stars doing it, but I think I could do a more convincing job than those 2 soldiers in the video.
I don't think this is "proof" that Source engine 2 is in development, The fact that valve code uses these flags/keys to determine which engine to use doesn't mean both engines even exist. This line increases their code's overall engine portability, maybe in a future sense, kind of like "Let's...