When Sony began applying for a new SKU back in May it seemed they were only going to change the Wi-Fi antenna and improve the Bluetooth, but now it seems the new SKU will boast a 1 TB HD as well.
The CUH-1001A is the current PS4 launched last year. The CUH-1001X is the new PS4 waiting on the FCC for approval. The "X" symbolizes a change in HD size. The new SKU supposedly will be sold Q4 2014 and will likely come as a bundle to keep up the sales momentum.