The revision of the console has been anticipated for some time now, but Giant Bomb claims that the new hardware will feature an improved graphics chipset, doubling the shader core count from 1152 (18 CU) to 2304 (36 CU) and increasing the core clock by over 13% from 800MHz to 911MHz. The PS4K release date is yet unknown.
The new graphics update should put the total theoretical compute performance at just over 4.1 TFLOPs. This is comparable to an overclocked AMD Radeon R9 380X, but until we know if anything will change with regards to memory, it could have less memory bandwidth than the latter.
The CPU is also set to see a slight increase in clock speeds, from 1.6GHz to 2.1GHz. We believe this increase in performance should make the PS4K competent at rendering games at 1440p, but we are sceptical as to whether this is really enough for gaming at 4K.
Sources:  http://www.giantbomb.com/articles/sources-the-upgraded-playstation-4-is-codenamed-ne/1100-5437/