He was holding off A.I. due to reasons that he wanted to wait for computer technology to advance. His plans was to begin filming A.I. right after completion of Eyes Wide Shut. There are rumors though, that Kubrick never really did complete the story for A.I., that he never found the story he really wanted to film. There is some truth to this in all the different science fiction writers he went through in trying to collabarate and all the unsuccesses. And then there is the starting point of what he concieved the story to be, in that it would be a focus on three different natural elements: fire, water and ice. The finished product, by Speilberg, feels like an ode to the life career of Kubrick with how so many different things in the film feel like they are borrowed from a previous Kubrick film so there definitely may be more truth to this than possible.
In the late 1960s, the Beatles approached Kubrick to adapt Lord of the Rings into a movie and he declined calling it "unfilmmable."
There is one project though, that I hear faint things about right after he died, that I never heard of any since. All I remember from the rumor is that Kubrick, in inspiration from Kieslowski, was going to write, or help adapt, or help finance a french movie that was going to be made. The story was said to be a very basic one dealing with just today's world and was said to be inspired by Kiewslowski films. I completely forget the storyline, but I remember it was a story and project Kubrick had his name to.