In addition to Feature Services, please allow data to be published as a Dynamic Map Service.
ArcGIS online seems to be missing dynamic map services. These services provide useful functionality such as dynamic labeling which currenly does not exist in Feature Services and very hard to control in Tiled Services.
This will allow web maps to contain "nice looking labels" that will move based on map extent. This is different to the tiled cached results of labels in which cases the labels might exist on tiles outside the current visible extent and the user does not see it.