This is an insightful observation. Designing more and more complex systems to achieve high availability may end up not achieving anything or even being negative

This is an insightful observation. Designing more and more complex systems to achieve high availability may end up not achieving anything or even being negative because those HA systems are too complex to implement, configure and operate in a way that actually achieves HA. I think the same may end up being true of globally distributed databases that try to provide generic ACID transactions. Will they actually ever achieve the performance and reliability needed to serve massive scale global work loads? Or will this be a Mongo situation where all of the scale promises turn out to be unfulfilled once you actually reach the scale where you need them?