I was just thinking the same thing. Dark Sun really needs a fixed Year Zero starting point. One where things are generally pretty bad, but on the cusp on change here there and the other place. Situations only waiting for a band of plucky heroes to come along and tip things into action. And then future supplements never try to advance past that Year Zero point, they just fill in more location details or background info.
The last thing you want for Dark Sun is a metaplot that goes around fixing things and taking out all the major villains.
I doubt we'll have to worry about "future supplements" – Wizards starting with 4e hasn't been particularly fond of "sub-product lines" the way we had in 2e and 3e. If we get a Dark Sun book, and it seems we will, we'll get
a Dark Sun book and then they'll open it up on the DM's guild. Possibly two if they're splurging (player's book and DM's book + adventure).
To be perfectly honest, most settings benefit from a Year Zero continuity. TSR pushing Metaplot changes to Dark Sun, Ravenloft, Planescape and Dragonlance did a lot more to damage those settings than help them. I don't think of many people who look on the The Greyhawk Wars, Grand Conjunction or Faction War with warm feelings.
I'm in the minority among Dark Sun fans who believe that the post-metaplot Dark Sun setting is a better setting than the original, mainly because there's more variety among the city-states of the Tyr region and because the setting expands beyond that. You still have three city-states ruled by sorcerer-monarchs, but you also have a fake sorcerer-monarch (Draj), anarchy (Raam), fledgling democracy (Tyr), and merchant council (Balic). You also have some interesting threats on the horizon, with undead to the south and the thri-kreen empire to the west that just got a convenient way of getting off their grass plains and hitting the Tyr region. There was apparently also some meta-plot about the original life-shaping halflings making a comeback, having been off in space in the Messenger comet, but the line was canceled before that became official.
Metaplot is a cynical ploy to try and force players to buy every product when it comes out in order to keep up.
I agree that metaplot is generally bad, but I don't think the point of it is to try to force players to keep up. What I think it is is game designers wanting to be storytellers, so that's what they do. In the specific case of D&D, I also believe that the novels generally made the company more money than the game stuff (at least in the short run) – I believe
@JLowder used to work in the TSR book publishing department and discussed that in some threads – so when the needs of the novel line and the game publishing line collided, the novels tended to win.