I have developed Solution Explorer Enumerator in my VS2015 extension using ISVHierarchy and ENVDTE. I process each item in the solution based on its type as shown below. References Folder is not caught by any of the checks below.
What is the recommended way to detect References folder?
If TypeOf Item Is Solution Then
....
ElseIf TypeOf Item Is SolutionClass Then
....
ElseIf TypeOf Item Is Project Then
.....
ElseIf TypeOf Item Is ProjectItem Then
.....