The downtown leg is slated to be completed in 2008. The airport extension hasn't been scheduled yet; it's still being discussed and planned, so it's doubtful it could be completed within the next ten years.
We'd also like to see an extension run to the north Strip, perhaps down Riviera Boulevard to the Stardust/Westward Ho/Circus Circus group. And while we're dreaming, how about spur lines into the suburbs along Sahara Avenue, Flamingo Road, and Tropicana Avenue? The monorail that ate Las Vegas!
Seriously, this transportation system has been getting kudos from almost all reviewers, observers, and riders. Now it's just a matter of seeing if it turns a profit.