FujiFilm GFX 50S To Begin Shipping in Februrary for $6499

[Jopa]

Maybe some people just want the best image quality or a certain look

It does have that certain look, and I'm trying to figure out what it is That somewhat "3d look", right? I'm not sure 100%, but I think on FF it can be achieved by stopping down a fast lens to whatever equivalent the MF counterpart offers. Let's say we're taking one person's portrait, and wide open the DoF is shallow so the person's contour will be OOF (something like one eye in focus only). If the lens is stopped down to the point the whole contour is in focus, but everything else is still blurred nicely - here comes the 3d look. Drop a little bit of light to the person and the separation becomes even more pronounced. The sharpness (in-focus part), glass characteristics, and the aperture blades shape (oof-part) are also contribute to the look. The sensor itself is irrelevant I think...
It's probably easier to achieve better sharpness using a large sensor (less demands to the glass), but other than that I don't think it's going to be a helluva difference between the FF and .79x crop.

Not that I would ever be in the market for something like this, but it only has FullHD video? Everyone lambasts Canon when they don't implement 4k 60p in every camera. Shouldn't a $6,500 camera with such a nice sensor be able to do 4K video?

Most likely the sensor is not capable to deliver 4k at acceptable performance cost. Remember, it was built by Sony in 2014 (I think). Anyway I don't think it will be a big deal for the potential buyers.