Hi David,
Scale Reference as you've described is not supported on the service of feature services nor has the functionality been built into the Map Viewer client. In order to enable this functionality currently, you can look into setting the symbology in ArcMap or ArcGIS Pro and publishing a tiled layer that incorporates the reference scale set.
If you require feature access, which it looks like with the network trace tool, you can look at adding multiple versions of the same layer that have the appropriate scale set, using scale visibility to control when the layer is visible and not in the map viewer.
I see you've already supported the following idea but I will post it so others can easily find it too: https://community.esri.com/ideas/12136
-Kelly