I think you mean "makes it impossible to know if a release includes backwards incompatible changes without looking at the release notes, while still having a release number say nothing about other aspects of the significance of a release."
The compatibility guarantees of CockroachDB do not change with this. It's always been the same: version X+1 will remain backward compatible with X but may break compatibility with X-1. Deprecation notices for definitive changes in version X+2 are introduced in version X.
That is literally impossible; a breaking change from X-1 to X+1 must have been introduced in one of the intervals X-1 to X or X to X+1. It the latter, X+1 breaks compatibility, if the former, let X' = X-1 and X'+1 breaks compatibility.
Presumably you mean that X always includes warnings about breaking changes in X+1, which is a vast improvement on some projects, but knowing that a problem exists doesn't mean it doesn't exist.
No, that's not how it works. The deprecation is introduced in version X-1; the new behavior is introduced but is opt-in; in version X, the new behavior becomes opt-out; in version X+1 the old behavior is removed.