You know what I find funny? The Toy Story movies are essentially The Brave Little Toaster over and over again! the Brave Little Toaster is built around the theme of unconditional love, drawing parallels between God/Man, which I don't even think the Toy Story movies or even the Brave Little Toaster did intentionally. Good art will always hint at these sort of allegories even if unintentional because they are reflecting upon something that we see or experience in real life, and so a need of unconditional love from a higher being is going to naturally filter through! What I find fascinating is that I really think it is totally unintentional.
But Toy Story 3 was wrapped with such a nice little bow at the end, it really doesn't demand a sequel. This just screams "we're out of ideas, let's go back to what we were good at!" I also question if Pixar is introducing any new blood into their creative circle. The problem with sustaining success is that no one is an endless well-spring of clever storylines and ideas.... Even acclaimed authors only manage to squeeze out a few note worthy stories before descending into obscurity. What I fear about pixar is that their creative circle is suffering from a generational nepotism that makes it harder for the newer blood to breach the circle, this happens to every group and in so many other facets of life. Even if they can acknowledge that the new blood is good, it might not be 'their kind' of 'good'. They do still make great movies but It does feel like the salad days are over, they're probably going to keep on making above-average movies that score 80% fresh on rottenomatoes, which is fine, as they are by no means poor or untalented story-tellers. They understand all the fundamentals and more, but I feel that the youthful passion is now gone, and most of the 'old guard' probably have complicating family lives by now, meaning they're not sitting around at home or in the shower, thinking about ideas, they are tending to their commitments.