A much better file duplicate action default name in the editor would be to add an underscore _ before the last dot . if one exists.
For example index.html duplicated would currently generate a default name of index.html copy. The drawback to this default convention is that the user loses the syntax highlighting rules for the particular filetype being copied and potentially functionality. Changing the default as suggested, in this example would mean index.html would become index_.html. Furthermore index_html duplicated would become index__.html.