They don't actually claim it's fast or give any measurements of speed (apart from "ultrafast laser"). It seems reasonable to be on the order of other laser-based optical storage systems (CD, DVD, blueray).
EDIT see also https://news.ycombinator.com/item?id=6034075
Instead, longevity and data density is emphasised, and application for long-term storage. Sounds like a replacement for tape.
If the read/write/access speed is going to be good enough then perhaps it might replace HDD and depend on SSD as another cache level. The SSD cache would need to be page-file-based (just like OS caches file pages in RAM). block-based caching would be horribly inefficient in this case.
This also got me thinking about a filesystem for the 'superman memory'. It could be an extremely simple logging filesystem without garbage collection. Since the storage is supposed to be enourmous this could work for more than just a an incremental backup.
Instead, longevity and data density is emphasised, and application for long-term storage. Sounds like a replacement for tape.