Union Feature Layer — Group layers with identical schemas into a single layer; apply properties to group

[Bud]

It would be great if there were a way to group layers with identical schemas into a single feature layer. So that we could apply a definition query, symbology, labelling, etc. all in one place to the unioned layer, rather than to each individual layer.

For example, in my Optimize Route Event Layers idea, I talk about a workaround that has two separate layers:

1) Route Event Layer: for events that only pertain to a portion of the line.
2) Feature Layer: for events that do pertain to the whole line (uses the FC shape).
Both layers have the same underlying event table as their source.

Those layers have identical schemas. Could they be unioned into a feature layer, similar to how UNION ALL works in SQL? If so, then I could apply properties like a definition query, symbology, labels, etc. all in one place, which would be automatically applied to both underlying layers. That would simplify my map and prevent me from accidentally applying properties to one underlying feature layer, but not the other.