Pioneer are attempting to become the first to have an Ultra HD 4K Blu-Ray player on the PC market with the BDR-S11J-BK and BDR-S11J-X. Unfortunately, these players will only debut in Japan, but that's at least some progress. These Ultra HD Blu-ray players require some beefy equipment to power them, though.
Unfortunately, the only CPU that can currently decode PlayReady 3.0 DRM needed for 4K Blu-Ray viewing are Intel's Kaby Lake processors. You'll also need at least 6GB of RAM and a GPU with an HDMI 2.0a port, not to mention a 4K monitor or TV.
The two different Pioneer Ultra HD 4K Blu-Ray drive models will have slightly different features. The BDR-S11K-BK is the standard model, and the BDR-S11J-X is a quieter, high-end model with improved CD playback. Pioneer plans to release these new Blu-Ray drives near the end of next month in Japan. Unfortunately, there has been no plans to release the drives in the U.S. market announced as of yet.