Spanner seems to solve a different problem. It’s effetively a multi-master database where the leader election algorithm can be tuned to ensure that your masters are geographically close to where writes/reads are actually happening.

Many databases are “partitioned” by user anyway so in this case the DB can be smarter if it doesn’t have to handle cross partition queries.

Seems like the idea of partitioning a MySQL database taken to the next level.