Storage — Pluggable memtable implementations for things like fast memory storage and columnar formats.

Schema — External schema storage in a remote service such as etcd is now an option.

Authentication — This change allows for the Cassandra command-line tool, CQLSH, to use LDAP, Kerberos and other auth methods.

Network Encryption — Extension point, allowing external key providers (e.g. as HashiCorp Vault) to make key management easier in large deployments.

Guardrails — Restrict anti-patterns in your production environment:

• Disabling certain features.
• Disallowing some specific values, like limiting the number of indexes that can be added to a table.
• Defining soft and hard limits to certain database magnitudes.

Extensible to create your own!