the official timeline post, along with some concept art.
The blurb says the game was designed to be "the most realistic pinball simulation ever," complete with actual material physics and graphics running at in 60fps at 1080p (as you might have guessed from the title). There was also going to be a "Gran Turismo level of progression," designed to build as much replay value as possible.
This, says Insomniac, also explains the whole (pin)Ballz phenomenon, and the company's fascination with pinball in general. The developer will discuss the abandoned game on a future podcast. As for whether it'll ever return, Insomniac says, "The Zen Pinball games do a fantastic job anyways."