The property that attracts the most mission critical use cases is the ability to keep transactions rolling without loss of guarantees, even while hitting the typical cloud failure modes. Some applications can't make tradeoffs between correctness and global availability, for them FaunaDB's mainframe-like capabilities are key.
For the average application, the benefit is that you don't need to write code to address database drift / eventual consistency. I expect Fauna-like systems to gain popularity as more developers come to expect cloud-native solutions to offer global ACID transactions.
Well, I don't expect distributed ACID transactions to ever become a thing developers expect. I see people try them, but leave unhappy because of the unexpectedly bad latency and performance. Hence the lack of growth in trends.
Furthermore, eventual consistency was never problematic, it was just a myth. It was never hard, certainly not harder than ACID transactions in all those MVCC systems. So not much to benefit from for an average application. And today with all the research in strong eventual consistency applications can have all that correctness without coordination and without sacrificing performance, latency and availability. This is where the opportunity for distributed databases still exists, performance and latency are sellable.
For the average application, the benefit is that you don't need to write code to address database drift / eventual consistency. I expect Fauna-like systems to gain popularity as more developers come to expect cloud-native solutions to offer global ACID transactions.