This is likely a repeat idea, but I was having trouble finding exactly what I was looking for. I would like the ability to be able to add and remove layers to existing hosted feature services in ArcGIS Online without affecting the existing data and configurations (i.e. symbology and pop-up configurations). This would be helpful for data organization and management.
For example, I published a hosted feature service for habitat type monitoring. There is a unique layer for each habitat type because each habitat type requires a unique field schema. I published the layer and configured it in the web map, but then I was told that we needed to add an additional habitat type for this years round of monitoring. It would be nice to be able to add that to the existing service so everything could "stay in one place" rather than publish a new service just for that one habitat type.