Thank you very much for you remark about the scalability.
Personally I think that scalability is one of the strong points of the Pile-File. The binder with the documents, as shown above, is only used for the recent documents. As soon as the binder is full the documents are taken out, and a copy of the category sheet is placed on top. To keep the pile together you can use a tube clip fastener.
Even in the archived Pile-File you can still use the category flags, and you can still retrace documents using the document sequence number. (If you use this feature as described in the video). The documents in an archived Pile-File also retain their chronogical order, making it possible to find a document back if you know it's date.