I'm not sure if what you said applies, they have severe restrictions and spanner offers subset of MySQL functionality which is already bare compared to other da

I'm not sure if what you said applies, they have severe restrictions and spanner offers subset of MySQL functionality which is already bare compared to other databases. Changes can be done by primary key only, so it almost feels like a KV store that can do joins... I don't think it's easy to port existing applications to use it and in the end you will still need to accommodate shortcomings in your application.