The highest capacity optical disc on the consumer market today is Blu-ray. In standard form it can hold 25GB of data or 50GB if dual layer. Theres also been the recent roll out of the BDXL format, which increases that capacity to 128GB. But such levels of storage are fast becoming too small, and both Sony and Panasonic have realized this and decided to do something about it.
The two companies are teaming up to create the successor to the Blu-ray disc. Their plan being to have the finished, higher capacity optical disc ready for use before the end of 2015. As for how big that new disc will be, the target is to hit a minimum of 300GB capacity.
Even though we seem to be moving towards streaming content more than purchasing it on disc, theres still a need for optical media in order to archive data. Sony points to general data archiving, video production, broadcasting operations, and even cloud data centers as requiring high capacity optical media. Discs are also cheap to produce and remain viable for a very long time.
Movies are slowly going to start making the transition to 4K as the TVs become more commonplace and affordable. It seems likely 4K movies on optical discs would be desirable. For example, the first 4K movie you could download is 120GB. Add in extras and multiple versions (theatrical and extended cuts) and you can see why distributing on a 300GB disc may become desirable in a few years.
What technology this new optical disc will use is unknown, but Sony has pointed to their own 1.5TB XDCAM format (12 25GB capacity discs in a cartridge) and Panasonics 180TB LB-BM9 format (up to 90 magazines each holding 12 100GB discs in a cartridge) alongside RAID technology as key examples of how they are already pushing up capacities. Cartridges and multi-disc formats are unacceptable as a Blu-ray successor, but 300GB is the target, not terabytes.
Now read: How to start watching at 4K right now