Tableau Prep can already conncet to Excel, txt, csv etc.
Most business users either puts these files on a corporate shared drive or in a cloud drive like Dropbox, OneDrive for Business, Google Drive etc.
Once we begin seeing users connecting to flat files, they will all run into Tableau Server/Prep Conductor not being able to connect to their locally stored files, and then they will complain, A LOT.
Allowing Prep Conductor to connect to cloud drives will be a huge benefit in the adoption of the product, since it will be able to simply connect to the files in these cloud drives.
For Corporate shared drives, I assume the old "use UNC-path and allow read acces to Tableau Server Run As Account" still works.