Sony appears to be readying two new PS3 models, though the degree to which they have been changed isn't clear. Sony has filed for certification for two new PS3 models in South Korea. New models have also been seen on a webpage for Japan's Minister of Internal Affairs and Communications, indicating that they could be releasing region-specific models for Japan and South Korea.
The models, "CECH-4200" and "CECH-4205", are likely just small hardware changes rather than a major overhaul. Based upon the model number, it's suspected that they are of the Super Slim PS3 variety with updated CPUs using a smaller lithography or some other small update.
We've seen no new model numbers for the US, though it's possible they are coming. We'll keep our eyes out for any additional references to these, or new, model numbers.