P55 won't be the only chipset that Intel plans for mainstream Nehalems, scheduled for Q3 2009 and Q1 2010. The Havendale quad-core mainstream Nehalem is expected in Q3 2009, while the dual-core Nehalem with IGP, codenamed Lynnfield, will slip to early 2010. 

P55 does support Havendale, but we've learned that there will be at least one more chipset later on. We don't have any additional details about it, but we will do our best to find out.

The P55 should replace the rather hot selling P45 platform, while the new one might be a cheaper version of P55 to fill the gap.