I’m also seeking this as the OmniSync servers are not allow to be used by my employer. Having a single view point, but implementing cross domain data flow controls with data separation, and multiple sync back ends for different “folders” or “identities” (think Apple Mail/Contacts/Calendars/Reminders/Notes managed by MDM where the user gets a single pane of glass view to inform decisions, but the data isn’t co-mingled on device, different accounts sync to different back ends, and managed data can be prevented from flowing into the unmanaged space by policy). Its fair enough for an employer to not want work tasks to end up on Omni’s servers, but its also fair for me to not sync my personal stuff to a WebDAV server inside the company (and need a VPN connection to access).