The point of the SQL layer now merged into Spanner is so that people don't have to run F1 or something like it on top. I'd expect continual improvements there, especially if enough folks say "I'll move if X"
Not sure if "never", but from the new Spanner paper[1]:
> While we have seen comparatively little demand for this feature internally, supporting such semantics improves compatibility with other SQL systems and their ecosystems and is on our long-term radar.