Well, you will never see the real limitations of all the other options.
That being said I had too an interest for Cassandra and scylladb (even faster Cassandra) and I have some projects in other languages with these databases
I would like to play with them on b4x and I have made some wraps as a proof of concept. But that makes only 2 of us on the whole forum.
Download the Cassandra JDBC driver, configure the JDBC URL, and connect to DbSchema for ER diagrams, SQL editor, and schema sync. Driver setup guide with free .jar download.
There are a lot of studies - worth to get familiar with - eg:
1) VeronikaAbramova, Jorge Bernardino. (2013). “NoSQL Databases: MongoDBvs Cassandra”, Conference C3S2E. [Online]. Available: http://deliv-ery.acm.org/
2) Parker Zachary, Poe Scott, Vrbsky Susan. (2013). “Comparing NoSQLMongoDB to an SQL DB”, ACMSE’13. [Online]. Available: http://deliv-ery.acm.org/