Some of the use cases can be found here:

https://sirix.io/documentation.html

The main distinctive features are our main document store index, features inherited by ZFS (checksums in parent pointers, the main index, a trie, compression and hopefully soon encryption of page-fragments, always consistent on-disk, log-structured without the need of a WAL...), versioned user-defined indexes, highly concurrent data structures (every transaction has access to one snapshot and we only allow one read/write transaction, parallelization has to be done by the client code) and record-level versioning (also a novel sliding window algorithm -- whereas a slightly other implementation is patented by the founder Marc Kramis).

I might implement pointer swizzling for the upcoming 1.0.0 release, should speedup Sirix considerably :-)

https://sirix.io/features.html

I think XQuery is great for querying JSON data. That said in the future I'd also implement something based on Spark to distribute queries...