In terms of subject matter, fiction has long addressed the nature of reality. Science fiction has often examined reality and turned it on its head. Author Philip K. Dick was famous for this. He said, "In my writing I even question the universe; I wonder out loud if it is real, and I wonder out loud if all of us are real." He referred to himself as a "fictionalizing philosopher." Charles Platt says of Dick's work: "Everything is a matter of perception. The ground is liable to shift under your feet. A protagonist may find himself living out another person's dream, or he may enter a drug-induced state that actually makes better sense than the real world, or he may cross into a different universe completely."
Possibly taking this idea further, Alfred Bester attempts to utilize synesthesia in his novel The Stars My Destination. (Synesthesia is a neurological condition in which cognitive and/or sensory pathways get crossed, e.g. a sound is heard in response to visual stimulus.) Bester conveys synesthesia to the reader via unusual graphic images of text--almost giving the reader synesthesia in the process.
Fiction has been created that enables the reader to be even more active. I'm thinking of those Choose Your Own Adventure Stories in which the reader gets to make decisions at plot points. In recent years technology has enabled us to go further with this concept via software-driven Interactive Fiction.
This leads me to my point: I read a story recently that was written in an unusual way about an unusual reality. It occurred to me that perhaps it was the culmination of the ideas outlined above. Instead of showing an atypical reality, perhaps this story actually creates a new reality since the reader has to keep re-evaluating everything. It was mind-boggling and my description isn't doing it justice.
All this prompts me to wonder: How far could we go with fiction? What do you think?