The X48 will be the new high-end part, the P45 will replace the P35 and now the P31 is set to get a successor, the P43. Set to arrive in the second quarter of this year, together with the P45, the P43 chipset will be paired up with the ICH10 southbridge and feature support for the new 45nm processors.
Unfortunately, the 1600 MHz CPUs will not be supported officially (expect motherboard manufacturers to add support for them) by the P43 and neither will be CrossFire. The chipset will have only one PCI-Express 2.0 x16 slot and will support both DDR2-1066 and DDR3-1066 memory. Motherboard powered by the P43 are also expected to have less overclocking features than the P45 but even this will depend on what manufacturers will offer. Until P43 motherboards hit the stores though Intel still has the X48 and quad-core 45nm CPUs that need to be released.