it's actually 128GB per disk (BDXL), I only know of Chinese companies announcements of 500GB optical disks last year[1], not sure if they are already deployed to some enterprise partners, it's entirely possible. Their more theoretical research goes far beyond that. [2]
There are archival storage machines similar to tape drive robots for archival storage in the Chinese market where you have hundreds of such disks in a single unit and 1PB+ per rack.