With the powerful web APIs it has become relatively easy to create decoupled applications with Drupal 8 as a backend. A number of lighthouse applications have been created and powerful demo systems and starterkits such as 'Reservoir' und 'Contenta' have emerged.
Usually decoupled applications are used to display content, but editing of content still takes place in the backend.
However, technologies like React can perfectly be used to create a great editorial experience. Given the powerful REST APIs of Drupal a decoupled editing system can easily be integrated.