Either the Coen brothers wanted to use it too badly, or, most likely, they didn't notice, but in their new movie, when Llewyn looks at The Incredible Journey poster, he's seeing an ad for a movie that's two years in the future.
Is it the film's tagline, or the film itself that they were drawn to? Well, I'd guess a little of both. It could be a little tongue-in-cheek, but front and center on the poster is the cat, which could serve as an acknowledgment of the wild adventures of the unfortunate little orange-colored pet in this movie. Or could the animals indicate something about the slovenly nature of Llewyn himself?
More importantly, though, is the tagline, which reads "nothing could stop them...only instinct to guide them across 200 perilous miles of Canadian wilderness!" We see Llewyn reading these words, and clearly he's playing them in his head and finding some sort of meaning in them in relation to his own life. It may indicate that Llewyn, defined by his own defeatism, is going to find, rather than lose, determination to succeed. Really though, I think it's a bit darker than that. His narcism has left him with not much in the world by way of friends or a home, thus his journey through life is going to be rough, like the wilderness, and alone, with instinct as is only real friend. In a movie that's so careful about revealing information, the use of this poster could come across as a bit corny and intrusive. Isn't it essentially a thesis statement directly stating something about the protagonist? In a way, perhaps, but I actually think it works great in the film, especially when seen in the ironic and humorous light I imagine the Coens intended. It's a little funny to see Llewyn finally find some truth in...a poster for a kids' movie. After all, for a man so opposed to careerism, it's going to be things like this that help him get along through his rough and tumble world.