I don't think it will happen. There are two reasons for this. Sony knew what they were doing when they removed Backward Compatibility from the PS3. It wasn't because it was too expensive, it was so the consumer would have to buy a new PS2 becuase they sold their old PS2 when they bought the PS3, which means more money for Sony.
The other reason is Sony can put PS2 games on the PS Store and have people re-buy them, which again, makes more money for Sony. Sony is already putting PS1 games on the PS Store and they are selling very well and making a lot of money for Sony.
Why make a free software download when you can put the games on the Store and make money. Even though the PS3 can play PS1 games, PS1 download games are making a lot of money. A whole lot more people have PS2s, so the obvious decision for Sony would be to put the PS2 games on the store to re-buy so they can make all of that additional money.