The last part is interesting to think about. Check out what was said during the talk Gabe had with Geoff Keighley at GDC 2015 about source 2:
It's to make it possible for thousands of people or billions of people to be all generating this shared entertaining universe. You can look at the properties that we have and probably say oh I would see how having a whole bunch of people extending and annotating and storytelling in this particular universe would make sense. But now that we got Source 2 out now you'll start to see us start to lay out some of the pieces so that we have this really large shared collaborative entertainment space that allows people to be as productive as they want to be in terms of building entertainment value for other people. That's something that we started four years ago. We had these ideas about how you build these large endless entertainment experiences and one of the dependencies was getting a bunch of economy stuff working there's a bunch of tools work to do, those are baked now. Now we are going start capitalizing with with how that actually translates into entertainment experiences for people.
I figure there will eventually just be a Half-Life that is some rolling perpetual thing, much like all the other "service" games they do. Probably a decade away though