So it sounds like you are wanting the ability to select a file from an predefined directory? Then the user can select the file using some kind of file browser where you can drill down to select the file you want?
It would be cool if someone made another module that can either extend the core imagefield or create a new fieldtype to allow for different sources to be added via additional modules?
I've used something like this before in Drupal with the https://www.drupal.org/project/filefield_sources module. You can see all the modules that integrate with it at https://www.drupal.org/search/site/filefield sources.
In the screenshot below, you can see the different toggle links/tabs that are added: Upload, File Browser, Reference existing, Remote URL. Each additional module can add more toggle links to change the input that is used. Sources are configured per field in the field settings.
If we had a module like that, then we could create an another integrated module that adds a "File browser" source link/tab that uses an input similar to the "Page List Select Multiple" input field type from the core Page Reference module, but instead of pages show/select files and folders?
Maybe the input could look something like this?? Taken from PageListImage module at
There is also already a module to select files, but maybe it could be modified to add a new inputfield type similar to image above?
Or maybe you could have a module like https://www.drupal.org/project/imce and https://www.drupal.org/project/imce_filefield that just adds a "Open File Browser" link to the image field that opens IMCE or similar to browse a file system? There is also https://www.drupal.org/project/visual_select_file that has a slightly different UI.
I know this isn't a solution, but these are all rough ideas of me thinking out loud in case any one wants to run with it?