What's the difference between Drupal 8.0.x and 8.1.x?
The answer is semantic versioning. The "1" in 8.1.x, represents a branch that can contain new features as well as bug fixes. Backwards-compatibility to code written for 8.0.x is inherent in the numbering system. So, if your code requires features in 8.1.x, you should develop against it, but note you won't be able to deploy your code until 8.1.0 releases.