MariaDB 10.1 had Cassandra Storage Engine which was developed for Cassandra 1.1.x. Back then, Cassandra provided a Thrift API, and that was what Cassandra-SE used.
Then, Cassandra 2.0 switched to using a different network protocol (and also changed the data model).
This task is to develop a Cassandra Storage Engine V2 using DataStax's C++ client library (https://github.com/datastax/cpp-driver).
MDEV-8947 was a previous attempt to implement this engine. Unfortunately it didn't even produce a skeleton engine.