The first part of your question: "Why did the CHAOS project stop?"
CHAOS was initially conceived as a yearlong endeavor: agents would experiment on our smaller sites for a year, and then move on to bigger and better things--either at SE or elsewhere. CHAOS was not built to be a permanent team within the company. It was almost like a training program in that the whole team was hired from outside of the Stack Exchange communities, so members cut their SE teeth on experimenting with ways to develop the smaller and younger sites in our network. Then the year ended, and agents moved on as planned. (37.5% of us are still kicking around this joint.)
Your second question: "Is there any hope of bringing it back?"
Maybe. There's always hope, I suppose, but it'd be more accurate to say there are currently no plans of bringing something like this back. One running theme that was discovered in the CHAOS days was that the model just doesn't scale. One person can't run that kind of activity on more than a very small handful of sites at a time--three or four at the most, but maybe just one if there's a lot going on.
CHAOS had 8 members. The network had 60 sites back in summer 2011 when the team came on board and that number has more than doubled in the years since. We could never have enough firepower on the team for constant driving of activity, both on the sites and outside of them as more marketing-y type activity, on that many sites. (Well, we could, but then CHAOS would comprise... *counts on fingers*... about 25% of the entire company.)
- CHAOS wasn't big enough to provide effort to every community, and
- It wasn't worth it from a hiring perspective to make the team big enough, but
- Only working on a handful of sites at a time out of our huge (and growing) network seemed ineffectual, so finally
- CHAOS worked on figuring out how to provide ammunition to every community instead of individual efforts to drive activity.
The big lesson of the CHAOS project was this: Counterintuitively, hiring a bunch of people to do the work of building community engagement and activity doesn't work. What we needed to do (and what we ended up doing) is learn how best to coach the communities to build themselves, and that's why the members of CHAOS who stuck around eventually got folded into the Community Team.
So would we ever do anything like the CHAOS project again? Again, the answer is maybe. We learned a lot from that year and would probably learn even more if we did it again. But we don't have any plans to do so in the immediate or near term future.