While optical discs like CD and DVD might lose popularity over streaming media, the Blu-ray format is thriving. That's thanks to the fact that the discs named after the blue laser beam that reads the digital information from the round plastic slices are able to hold high definition content. Many users around the world still don't have access to high-speed internet connections, so Blu-ray is a good way for them to watch HD content. But the world is moving on and 4K or Ultra High Definition is rapidly gaining popularity.
Ultra HD promises two times the resolution of HD which means increased picture quality, especially on large screens. It also means that more storage capacity is required to store the content. Blu-ray currently offers about 50 GB per disc, but discs up to 128 GB are commercially available. That could be sufficient for Ultra HD movies and therefore it would make sense to put Ultra HD content on Blu-ray discs. The Blu-ray Association (BDA) also had this idea and they have said in an article on Techhive.com that Ultra HD on Blu-ray is in consideration. To move forward, the BDA has created a working group that has to find out if it's really technically feasible, if there's a market for it and how it would impact the existing installed base of Blu-ray players when an Ultra HD movie is inserted.
All with all points to consider and that's exactly what they do. In the meanwhile Sony Pictures has announced on CES that it will start selling Blu-ray discs that are labelled as mastered in Ultra HD. These discs are in the HD format but Sony claims that you'll see extra details due to the fact that Ultra HD equipment is used.