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.
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/