Sony have confirmed a plan for a form of backwards compatibility for PS2 games on PS4, as quoted by Wired.

“We are working on utilizing PS2 emulation technology to bring PS2 games forward to the current generation,”

No further details were given.  This comment, however, confirms recent speculation on Sony's planned use of emulation, which has been caused by the inclusion of 'four Star Wars Classics' in the recently launched PS4 Battlefront bundle.  Thankfully, the comments by Sony suggest that the scope is much larger than a few Star Wars titles as a pre-order bonus.

With little more information, we can only continue to speculate on the details of the announced emulation technology.  Whatever the case, the ability to play old favorites on our PS4 is something to get excited about.