This new case is called the CoverReader, and it is a new product from the Ukrainian ereader maker Pocketbook. I don't have details on the screen resolution yet, but I do know that this isn't an E-ink screen.
The 4.8" screen is made by PlasticLogic, makers of the ill-fated Que ereader. It looks they found a new use for their screen tech, and it's one where their tech is actually better suited for the purpose than an E-ink screen. Plastic Logic's screens have a range of benefits – such screens are flexible, shatterproof, ultra-thin, ultra-lightweight, power saving and daylight readable.
Update: It looks like Plastic Logic's press release may have gotten ahead of itself. This first model has a glass backplane with an E-ink screen, not the plastic backplane that Plastic Logic is famous for. That means that the first CoverReader units won't be nearly as sturdy as the later units.
Unfortunately, I don't have the more important details like price, release date, or screen resolution; they weren't shared by Pocketbook. But I do know that Plastic Logic will be making the new 4.8" screen in their Dresden manufacturing facility.
Update: This case is expected to be released in October 2013 with a retail of 99 euros. I can confirm that the secondary screen uses the CPU and battery of the smartphone and cannot operate without it. I can also tell you that Pocketbook plans to release other cases for other smartphones including ones not made by Samsung.