There’s Locomotion Studies which points in the direction of free aesthetic experimentation with moving things.

Primordial Dance and Liquid Selves go in the direction of creating abstract imagery by the use of different image functions.

Panspermia and Evolved Virtual Creatures show how to evolve plants and animals through a limited set of shapes. These are important for how they attempt to simulate living things that don’t attempt to mimic current species.

Sims goes further than UPA by coming up with creatures that are unique and aren’t based on real ones. This is not the case with anything done by UPA. What Karl Sims has shown is important: animation can proceed aesthetically from its own merits. This is true regardless of whether you make real looking trees or fake ones. Reality and unreality are in a sense meaningless here. The key distinction is whether you work with relevance to our lives, to our history. To take a more mild example, it’s one thing to create a tree, another to decide which real tree you’ll create, like an elm or a pine.

Hand drawn animation, it’s true, will probably never recreate the look of reality. Before computers, that role had gone to Paint on Cels. If somebody wants to go as far towards imitating reality as they can in hand drawn animation and there’s some method to their madness, let them try. For most though, reality is there to be incorporated where it works. A character with two hands that look different is the more important reality than a character that looks real but has hands that are mirrors of each other.

Generally speaking, most ideas a person is likely to concoct would work as well in any medium. It’s a good idea not to focus on the medium too much. Gerald McBoing Boing could easily have been done with wire figures on top of colored pads on a tabletop while remaining much the same.