This is coming in the new version, 3.12, of 123 due out this month. You can also join the Early Adopter program to try it now.
Dynamically loading choices from feature services
The search() appearance allows you to query ArcGIS feature services and populate choice lists based on the results of the search query. When using the search() appearance with ArcGIS services you can use @geopoint, @geotrace, and @geoshape for the searchColumns depending on the geometry of the feature service you are querying.
For search type the following searchTypes are supported, this list comes from the spatial relationship parameter when querying a feature service or layer :
This assumes being online of course. There will also be a way to link to online csv files.
Hope that helps