It reminds me of Matt Groening's theory that every great character must come with a stand-out silhouette.
I see that "theory" applied to Matt Groening a lot, and while he is a well-learned artist, really it's a long standing design principle when it comes to characters for illustration and animation. Matt Groening is just very good about promoting awareness of strong fundamentals in artists because the industry gets a lot of animators who come onto the scene with unique style and ideas but poor understanding of silhouette value and posing.
No comment on if there's gonna be an animated short before the movie?
Lava is the theatrical short that will precede Inside Out.