Intel changes its chipsets every year. The new chipset usually launches in late Q2 and lives until Q2 the next year. This cycle was a bit different, as this time around Intel made two high-end chipsets, X38 and X48, while it usually has only one.
This will not disturb the plans for the upcoming mainstream chipset, which will be known as the P45. The main feature of the new chipset will be PCIe 2.0, something that no previous mainstream part from Intel has had so far. The G45 chipset will also feature PCIe 2.0, but this is likely to launch slightly later than the P45.
Intel was first with PCIe 2.0 support on the X38 chipset, and AMD followed with the 790FX chipset. Nvidia is last with the 780i for Intel, and the soon-to-launch 780a for Intel will once again be first with a mainstream PCIe 2.0 chipset with the P45; and this time there will be dual x8 support, as well. You will just have to wait for late Q2 to see it in action.