To enable file access/management both within our App and external to it, I am trying to build a file management process that will have our Mendix App interacting with a traditional folder structure on a network file system, OneDrive, S3 or the such. (vs Mendix File Manager, where the files are uploaded and are only accessible through the App). Has anybody built this kind of capability?
Have a look at these module from the marketplace that provide de functionality you are talking about for Azure and AWS S3:
Other connections like OneDrive should be possible to implement in a similar fashion. Accessing network drives is more difficult due to the permissions on these locations, so the complexity there is how you woould be able to access the drives on the network from the cloud.