They will be split into two markets: mainstream and enthusiast. The mainstream models will replace the current LGA1156 'H1' Clarkdale and Lynnfield CPUs (Core i3 and Core i5) and will use LGA1155 'H2' packaging.
Yes, that's right, LGA1155 - one fewer pins than current LGA1156 CPUs. These sockets are NOT compatible, so you cannot use an existing LGA1156 CPU in a new motherboard or visa versa. Not only is the position of pin-1 different, the socket notch has moved from 9mm to 11.5mm from the centre and the entire voltage plane layout has changed.
So both Nehalem/Westmere sockets are now going to be obsolete at the end of the year. Note this is non-official, but the writings on the wall at this point.Next is Sandy Bridge 'E' (Enthusiast or Extreme, take your pick) 'Patsburg' platform, which features a huge new LGA2011 socket to replace LGA1366 in Q3 next year (although right now that seems dubiously convenient given the year of launch).