Hi Michael Block,
as enumeration values are static and defined in the modeler you could build that kind of UI using the out of the box features of Mendix. To do so you must somehow create the dropdown for each enumeration value. You could use a group box, tree node or build that kind of UI using a helper entity.
Inside that dropdown you place a list view or grid that is filtered by that xpath.
If you want to have something more sothisticated you could build your own pluggable widget. There you can map through all enumeration values using JS.