It's so disappointing that if you use even the most basic of SharePoint functionality (i.e. required columns) that syncing doesn't work and I hope that this is something Microsoft will work on. I'm not sure that the Fall Creators update will help as I think that when you access an online only file from Windows Explorer it downloads the file to your C: ... and if that file has required meta-data I'd assume it will do it as read-only. I'm hoping I'm wrong so please let us know what you find.