Indeed, I hope we can add such support in the future. There is one big issue with OneDrive, though, which is that it limits the length of a path to ~218 characters (see: https://excel.uservoice.com/forums/304921-excel-for-windows-desktop-application/suggestions/10733559-increase-the-218-character-filename-length-limit-t), thus the folder will have to be fairly high up in the folder hierarchy to avoid hitting the limit.
The discussion you refer to might be this: Dropbox Sync
In there, you will find some instructions on how to use OneDrive, though it will not work on iOS… which of course is exactly what you want 
I’ll update this discussion when we have more options for sync!