For the time being this is simply a rumor, however, French site JV247.com (linked above) is reporting that a game publisher told them Sony was planning to add PlayStation 2 backwards compatibility in a recent PlayStation 3 Firmware Update... but pulled it at the last minute.
They continue to mention that it may be added in a future update, and that we may see PlayStation 2 games on the PlayStation Store.
Adding fuel to the rumor is news that the original Medal of Honor and the ESRB-rated PlayStation 2 game "Rayman 2: Revolution" are slated for the PlayStation 3, which usually means they're going to pop up on the PlayStation Store at some point in the future.
As always, more details to come as they are available! More PlayStation 3 News...