I had a few aspect on working with X-refs:
- Drawing Views
when working with X-Refs (e.g. the Model the Environment in a Separate dwg, or split up in Construction Phases), it was a good option to be able to select, which X-Ref may be included in the drawing view (eventually mark them as reference to show with dashed/watermarked in the view). This information should be saved with the View and might be edited such as the scale, etc.
- Numbering
it were also a good option to include X-refed elements in BOM-Exports (or not - decide at export).Having a master model, the numbering should optionally number items in XRefs too, to avoid potential duplicates without the need of Prefixing the part numbers.
- Connections
Cross-Xref connections in the master model to assemble them together if needed
Maybe these aspects are worth of consideration 
BR,
Daniel