Yes it is conceivable that KZ3 could be ready by Fall of 2010 but I would be completely shocked if they released it that early. Here's why...
1. There's no way Sony will release both of their flagship FPS titles at the same time. Despite the 4 month gap between R2 and KZ2, some could argue that the games still cannibalized each other's sales. Sony will likely follow Microsoft's strategy of alternating their shooters each fall (Gears of War, Halo 3, Gears of War 2, Halo ODST). Even though Resistance 3 hasn't been officially announced and probably won't be til early next year, looking at Insomniac's release schedule on the PS3 all signs point to R3 coming out next fall.
2. As we saw with their work on KZ2, Guerilla are perfectionists. At this time they are still working their butts off on patches and new DLC. I don't see them ramping down support on KZ2 anytime soon to rush KZ3 for a holiday 2010 release. Even CoD W@W, which many felt was a disappointment, took 2 years to develop despite using a completed engine.
3. Sony loves to build hype years in advance. Look at the anticipation and wait time for KZ2, LBP, GT5, GoWIII, Heavy Rain, etc. I could see Sony releasing a huge teaser trailer at E3 2010 for KZ3 to get the hype train rolling and then follow that with a steady stream of gameplay trailers and screenshots similar to what they're doing with GoWIII right now. Hopefully with the success of KZ2, there will be more mainstream hype for KZ3.
