[Update 10:25 am: a reader asks if no new development "in the near term" could still encompass starting construction this year? That's not ruled out, but if they were confident they could start this year, they would've said so.]
If arena construction doesn't begin until 2010, there's no way the arena could open by 2011, which has been the most recent official opening date (though there's been some hedging).
It's even questionable that the arena could open in 2012. Sure, a 24-month arena construction schedule would allow a 2012 opening, but the Atlantic Yards arena--at least in its earlier incarnation--was supposed to take 30 or 32 months.
[Update 2:55 pm: See comment that construction this year shouldn't be ruled out. Even if so, I'd bet that 2011 is still not tenable.]