We work alot with Xref drawings (normally 4 drawings at a time) and would like to be able to have the option to promote one of the Xref drawings to the Master drawing and make the Master an Xref.

Master ..................> Xref 2
Xref 1 ..................> Xref 1
Xref 2 ....promote...> Master
Xref 3 ...................> Xref 3
Xref 4 ....................> Xref 4

We used to have the facility in a product called ISICAD before we moved to AutoCAD and Archibus/FM.
Don't know if other users would find this useful but it would save us alot of time closing and opening of drawings.