One of the two leading manufacturers of tape cartridge storage, FujiFilm, claims that they have a technology roadmap through to 2030 which builds on the current magnetic tape paradigm to enable 400 TB per tape:
https://www.anandtech.com/show/15888/400-tb-storage-drives-in-our-future-fujifilm
https://www.anandtech.com/show/15888/400-tb-storage-drives-in-our-future-fujifilm