These are the takeaways:
- Things have changed towards immutability
- Versioning allows a changing view of objects with immutable backing
- Increasingly, systems are based on writing immutable data
- Immutability extends consistent relational systems
- Semantically immutable data may be changed for optimization
- Immutability is the backbone of emerging "Big Data" systems
For me, with the personal experience of moving a system from a SQL-based data store to NoSQL, it is very interesting to Pat's talking about immutability and versioning because that's essentially the solution we took to get to a more scalable solution.
Also, what killed us when thinking of geo-replication in my experience on a NoSQL store was the linear version, which is strongly consistent, like Pat mentions on the takeaway slide. Going for what he calls a Directed-Acyclic-Graph (eventually consistenty) history is definitely a better approach for scalability.