Recently on his twitter page, Robert Bowling of Infinity Ward, or FourZeroTwo, recently denied the validity of a YouTube video showing potential new maps, accessed using a JTAG Xbox 360. As you can see above, he denounced the video as 'very fake'. The video seemed to show several maps, including Oil Rig, Shipment of Call of Duty 4, Fuel (released in the Resurgence Pack today), and DC WH, presumably a White House based map, as seen in the campaign.
I can't see why Infinity Ward would turn down a 3rd DLC Map Pack, the money they are making from the Stimulus Package alone should be enough to tempt them, and squeeze as much money as possible from Modern Warfare 2, over a half a year on from it's release. Again, I'd be very disappointed to find maps already on the disc, being sold to me for extra cost, hopefully it won't turn out that way.