Sony said that this feature will not be coming back, commenting to Ars Technica that it simply wasn't a strong selling point - contrary to the opinion of many. They may be right, considering the recent surge of PS3 pre-sales following the introduction of the Slim and a price drop. However, you might also keep in mind that the PS2 is still very popular, easy to obtain and relatively cheap.
Backward compatibility may not be a big concern for many PS3 owners because most likely have a PS2 anyway. As the PS2 ages and becomes less available in the market, things may change. Five years from now, will Sony regret leaving this feature out?
In related news, Sony has confirmed that their PS3 Slim bears a new 45nm Cell processor.