Yes, only a couple of cameras appear to so far be compatible with the UHS-II cards. Time will tell how that progresses.
Further to this, when Dpreview reviewed the D750 the writer was disappointed in how quickly the buffer filled when he used "an insanely fast XDSC card". In fact he used the SanDisk UHS II 280MB/s card thereby reducing the performance of the camera and so was getting significantly slower write times compared to the UHS I 95MB/s card he should have used.
http://www.dpreview.com/reviews/nikon-d750