I hope MN3 could Support Webdav Sync and all your requests achieved as various of CloudDrive is supported by Webdav. Meanwhile, we love Google Drive, Dropbox. But you know, in the Apple platform, the iCloud sync SDK is Easiest to implement and repair. For example, Notability has big and powerful Dev. Team, but still only support icloud sync. Need to be clear, sync is diffirent from backup. as backup to any cloud is simple but sync technique is very complex.
Even now，MN3 icloud sync has many problem to be repaired. We expect to give you guys a perfect icloud sync experience first and then try to add others.
Else，If you just need a backup tool to save files in Dropbox or Google Drive, this is easy to achieve.And already put into our suggeest board.
MN Support Team