We know that FR is the 2008 setting and Eberron the 2009 one. That's 2/3 of the official 3e settings covered by 2009, leaving Greyhawk as the only official 3e setting not yet published in 4e. I'll estimate that WOTC will keep up something roughly like their 'one a year' projection for at least two or three years, giving a low-end estimate of 2 or 3 more settings. Greyhawk, as the most recognisable of old-school D&D settings will be a strong contender for inclusion in those 2 or 3, but Dark Sun--as probably the most popular non-supported-in-3e setting on ENworld and RPG.net* and as a good fit for PoL--would also be a very strong contender. If I were a betting man, I'd bet at somewhat worse than even odds that we'll have Dark Sun by 2012. I'd demand slightly better than even odds (maybe 3:2 or 2:1) for DS being the first setting after Eberron and I'd take evens on DS being the first or second after Eberron.
*Obviously, there are other contenders, particularly Planescape, but IMHO and in my very rough estimate based on reading forums, Dark Sun would take top spot.