The example use-case (deferring initialisation of unneeded components of a spawning spaceship until required) is trivially solved with regular threads, but after reading more of the article I think they have much greater ambitions.
The use of fibers is emblematic of the way they have developed the engine 'on the go'. Whenever they implement a new feature, it is implemented on a per parent-object basis. This was okay when there were only a few ships and one location, so the copy/pasting was relatively minimal and trouble free. As they kept adding new content, it made implementing features a huge burden and forced them to come up with 'Object 2.0' (which provides a framework to 'macro' in features as needed). The side effect is that there is no real separation of concerns, and everything is poorly encapsulated. It has also led to a combinatorial object explosion, with everything simultaneously doing its own thing... poorly.
Untangling the big ball of
would necessitate a rebuild of the engine and game assets, which isn't going to happen. They have realised that a lot of the game/object data is 'sparse', and only a small amount of it needs to be running at one time. It seems like the solution is to split up the game into logical chunks by sticking each parent-object inside its own fiber. So you end up with ship fibers, landing zone fibers, point of interest fibers, planet_surface[x, y] fibers... with the idea that you'd just freeze and unfreeze each fiber wholesale, rather then having to manage the individual components inside the chunk of .
I can see this becoming the basis for server meshing. They could extend the fiber functionality to allow fibers to be transferred between servers. So as a server reaches 100% utilisation, they could spin up a new server, transfer half of the active fibers, then transfer the relevant players over. While none of this is exactly seamless, you could see how someone might come to the conclusion that fibers are a solution to the pile CIG has created.
CIG has made a ginormous batch spaghetti, so why not split up the spaghetti into individual containers of spaghetti, stick them in the freezer, and then thaw as needed. That way everybody gets a plate of spaghetti when they want it and when you no longer want spaghetti, you can pop it back in the freezer for the next person. It also means you can cook more spaghetti to freeze without worrying the old spaghetti. This is a very good and sane plan and we can foresee no problems with juggling a million containers of frozen spaghetti.