Currently, both companies make and market high-capacity optical disc storage formats that require a series of 25 to 100GB discs packaged in an "array" or "cartridge". A single 300GB disc option, would be more compact and convenient, not only as a higher-capacity single disc storage option, but require the use of fewer discs in a larger capacity storage array.
Of course, with Sony and Panasonic involved, you can bet that data storage isn't the only thing on their minds, especially with 4K Ultra HD and eventually, 8K video becoming a part of the home entertainment landscape. The larger file size requirements of both 4K and 8K could take advantage of the increased storage capabilities of such a disc. If applied in this manner, backwards compatibility with the current Blu-ray Disc format would need to be addressed as consumers would probably not warm to a new disc format requiring new playback systems.
Stay tuned for more on this story as it becomes available.
In the meantime, check out the official joint announcement issued by Sony and Panasonic as well as an interesting perspective on the implications this development from Audioholics.