Idea Summary
The "LOV Column Mapping Viewer/Editor" suggested (See attached Picture) is for "Creation/Updating/Viewing" of the text string pf "Additional Outputs" for a "Popup LOV" APEX page item, in case the LOV will be associated with more than one APEX page items. Currently, the developer must manually enter the string, which is time consuming, tedious, and easy to make mistakes. Most importantly, the readability of the string within the APEX designer is very poor, which makes code reviewing difficult (one would copy the contents and put it in a text editor for viewing/editing). The proposed "LOV Column Mapping Viewer/Editor" would make the complicated LOV composing rapidly at a much higher accuracy!

Use Case
The "LOV Column Mapping Viewer/Editor" would be used for developer to compose the text string of "Additional Outputs" for a "Popup LOV" APEX page item. It is only needed if a LOV contains/populates more than one data element. It is also used in code viewing to enhance the readability on the string of "Additional Outputs".
The same ideal could be easily applied into following 2 situations: (1) The Viewer/Editor for "Affected Elements" for Dynamic Action of "Set Value". In this case, the tabular contains only one column. (2) The Viewer/Editor for "Affected Elements" for Dynamic Action of "Disable" or "Enable". Again, in this case, the tabular contains only one column.
Preferred Solution (Optional)
To implement this function, a small button would be implemented at the end of the field of "Additional Outputs" for a "Popup LOV" APEX page item (or at the end of "Affected Elements" for Dynamic Actions of "Set Value", "Disable" or "Enable"). Upon pressing the column, the system would populate the "Viewer/Editor" with the comma delimited string value (if there is any). If the current value does not exist, the system would populate the "LOV Column Name" (for "LOV Column Mapping Viewer/Editor") based on the SQL for the LOV. The developer could either enter the "Return Item Name" manually or select the page item from a list.
Certainly, implementation of the suggested function would not eliminate the current manual entry capability.