I think there's a completely different story here, apart from the obvious (i.e. they'll wait until they've got something nice to show). Guerilla is originally a very small developer, much more suited to Killzone PS2 and the new PSP version than anything else. Right now they're finalising the PSP version, and the capacity to do a big PS3 project besides that is very limited. They will have started working on the PS3 version at the earliest say half a year before E3 2005, with at most the same amount of people that worked on the PS2 version.
Now, a while ago (as in somewhere Spring 2006), Sony infused a lot of money into the team, and they were allowed to recruit no less than 40 new people. Initially they tried to fill those in the Netherlands, but really, there aren't that many top coders around here - the gaming industry is still very young, and consists for a large part of Guerilla at that (which had fused together 2-3 other projects, among which Lost Boys). So that turned out to be a big problem, and they've had to look for talent abroad, willing to move to Amsterdam to work there.
So, my guess about how far along they are with the project is as good as any, but I don't think we'll see a game released before Christmas 2007, and they will be hard-pressed to show something decent by summer 2007.
The one factor I can't decide on how well it's going to contribute though, is Sony's new development setup, where they share development resources, code and what-not among all there SCE groups and regions. Guerilla should benefit from this and the state of current projects should allow them to catch up.
I personally think it might not be such a bad idea to licence the Resistance engine from Insomniac, and just focus on creating really great art for that, and let their techiest guys work on either hot tools, or further improving that already excellent engine.
