Loop normals are called 'Face-varying normals' in Alembic. Before this commit, the existence of such normals was used to enable smooth shading. This is incorrect, as the normals could encode flat faces just as well.
This commit adds the loading of these normals as custom loop normals. It then also enables Auto-Smoothing on the mesh (which is a bit of a misnomer and indicates to Blender that the custom normals should be used).
This introduces a new feature and changes the interpretation of certain properties in Alembic, so definitely aimed for after the 2.80 release.