It looks like IW will not be developing COD 8. A company called Sledgehammer Games (founded Nov 17, 2009) looks to get the chance.
Call of Duty 7Call of Duty 7 (working title) was leaked as being in production when David Kim, a senior animator at Treyarch, stated on a website "I am currently on my second title as a senior animator in the games industry with Activision / Treyarch on Call of Duty 7." Activision confirmed in November 2009 that a new, yet-to-be-named Call of Duty game will be released sometime in 2010. The game is rumoured to be set during the Vietnam War.
Call of Duty (2011)An unnamed Call of Duty game is under development by Activision studio Sledgehammer Games, and set for release in 2011. The game will reportedly "extend the franchise into the action-adventure genre". No other details were made available by Activision.
http://en.wikipedia.org/wiki/Call_of_duty#Main_seriesHere is more on the topic:
Activision's New Plans For Call of Duty Include New Developer, New Genreshttp://kotaku.com/5484026/activisions-new-plans-for-call-of-duty-include-new-developer