There aren't too many surprises with the Lumix S5IIX, it's essentially the same camera as the S5II, but with more codec options, USB-SSD recording and an all-black paint job. For professional video shooters, though, this new model could offer exactly the improvements that they need. The price difference, for what's on offer, is very reasonable, too. At the time of writing, the S5IIX will only set you back an additional $200 over the standard model.
Professional all-black look; Internal ProRes recording; External ProRes RAW and Blackmagic RAW support; USB-SSD recording; Not a huge price bump over the S5II;
Most won't need such high-fidelity codecs;