So checking Destructoid I found this odd rumor:http://www.destructoid.com/rumor-killzone-3-in-development-for-2010-release-152434.phtml

If it's true, isn't a bit too earlier?, but going for a logical viewpoint, A LOT of new game established on this generation are planned as a trilogy, and if you see the article it names also Resistance 3 and a sequel to World at War (World at War 2? take "at" out and you got the first game with an extremely straight to the point title).

Looking at the example of Resistance and Gears of War, if you have a console of choice and an engine ready, you can produce a sequel in 2 years, improving gameplay and visuals based on the structure of the previous games, If it turns true I can picture a pre-E3 or E3 announcement with fall 2010 release and delays to earlier 2011.

I still think is a bit sooner, either they need a huge boost to the online community or they want to finish the story, I hope is the latter but if is that, they need to focus a bit more on the writing and script, I watched all the cut scenes in KZ2 and so far I see the story not coming to the quality of the first, kudos to voice acting of Visari and Radec but still... I don't want to spoil it... but there was no way that Rico would do something as STUPID as what he did.

Rumors are rumors, so I don't take anything for sure, but common logic can tell you what to expect.