Hello Aaron,
The utility network is a services framework. That means we expose a set of REST APIs that can be consumed from multiple clients. The first client of those APIs was ArcGIS Pro, and other clients are catching up such as ArcGIS Runtime and Javascript API. ArcGIS Runtime 100.6 update will include the first cut of utility network sdk. Some apps such as collector and explorer will be updated in the future to support some sort of utility network capabilities based on the context of the app.
That being said, this doesn't stop users from writing their own code to hit those REST APIS directly. Take a look at this blog post I authored showing how can we use javascript to hit utility network api A technical walk-through for a simple utility network web trace tool with Javascript
EDIT 10/8/2019
UtilityNetwork API for Runtime is available on 100.6 read blog here
Hope that helps
-Hussein
