To the best of my knowledge, this is the Summit change history since 2008:
2008: Added a 10,600 BTU sear burner; added lighted control knobs; reduced cooking grate area from 693 to 624 sq in.
2009: Added the Tuck-Away rotisserie motor.
2010: Reduced the smoke burner from 8,000 to 6,800 BTU.
2011: Added the LCD tank scale on control panel; reduced the diameter of cooking grate rods from 9.5mm to 9mm.
I'm not aware of any news or rumors about when a new Summit will be available. There's a lot that Weber could do to update this grill, add competitive features, and improve durability of the design.