I'm not hyped yet, but even I think hl3.txt is fishy about how there would be this much data just for trolling.
Hell, lights.txt also made me curious. But it also made me think that will just not be all for HL3.
For a "realistic" day/night cycle, there's a lot more settings than I would ever expect.
You can put the Time and Date, set the Day Length, set a location and its timezone.
This is quite interesting because I've never seen this before, it's almost like you had a whole planet on your hands. And that isn't the only clue to this either.
You can set the length of the synodic month, which is basically the average time from when Earth, Moon and Sun are aligned (in this order), until it happens again, in other words, when the moon has gone full circle, to put in really simple terms. (It may be stuff they could have tried for SOB.)
From what I can see, Source 2 seems to be interesting enough because I don't think we have stuff that's not already working at this point at Valve.
Does not mean anything about HL3, but it means a lot about what Valve is trying to do in-house about their games and engine. And it sure looks interesting to me.
But I'm not hyped yet, I'd really want to see footage anyway. Or a teaser. That would be enough to shake the Internet really hard (and me as well).