Rumors suggest that the Blu-ray Disc Association will soon make an announcement regarding the availability of 4K movies on Blu-ray. A press release (in German) by German Blu-ray disc manufacturer Singulus has now given more strength to these rumors.
Singulus announced that they have successfully produced a test batch of triple-layer Blu-ray discs. Each layer has been further optimized to store 33GB, up from current Blu-ray's 25GB. The press release specifically mentions 4K movies as a possible use case for the 100GB discs.
High capacity Blu-ray discs are already available in the form of BDXL. However, BDXL discs are not compatible with existing Blu-ray players. While Singulus' announcement does not state clearly whether their triple-layer discs are backwards compatible (after a potential firmware or software based update), the BDA will clearly want backwards compatibility to exist, to allow a smooth transition to the new Blu-ray 4K standard.
There's also speculation surrounding the video codec that will be used for Blu-ray 4K discs. The existing H.264/AVC/VC-1 codecs used for 1080p Blu-ray will be sufficient for 4K content, if disc capacity is upgraded to 100GB. Nevertheless, a move towards H.265/HEVC may also happen.
While major Blu-ray backer Sony have opted to use the Internet as the distribution platform for 4K movies, the sheer size of 4K movies means that high capacity discs may still be the preferred way to distribute these ultra definition movies.