Sounds nice in theory, I would like to see few years of history of production systems using Spanner before we have enough evidence that nothing goes wrong with this approach.
While Spanner has only been available to be used outside of Google very recently (GA in May), it's been in production at Google across hundreds of products, including AdWords, since 2012.. with global consistency to boot...
(work at G)
Isn't that global consistency in effect frequently weakened because applications have to batch writes to get throughput? It's great to be able to have consistency, but in many other cases the source of inconsistency will largely just moved to outside of the data management system.
Sorry I don't have access to your internal incident tracker to draw any conclusion here. Will see in few years how this works out for external companies.
Plenty of Google's products use Spanner and have for years.