Off topic:
You have to love Microsoft. According to this (
https://blogs.msdn.microsoft.com/sync/2010/10/27/announcing-sync-framework-4-0-october-2010-ctp/), "The Microsoft Sync Framework 4.0 October 2010 CTP is built on top of Sync Framework 2.1 and it extends the Sync Framework capabilities of building offline application to any client platform that is capable of caching data."
Yet here (
https://msdn.microsoft.com/en-us/library/jj839436(v=sql.110).aspx) it states "Microsoft no longer supports the Sync Framework 4.0 CTP. All the functionality of SyncFx 4.0 CTP is included in the tool kit. You can download the toolkit from the download center."
Here (
https://code.msdn.microsoft.com/Sync-Framework-Toolkit-4dc10f0e) it does mention that the Toolkit supersedes 4.0 with this statement: "The Sync Framework Toolkit extends the Sync Framework capabilities for building offline applications, making it easier to expose data for synchronization to applications running on any client platform. Sync Framework 2.1 required clients to be based on Windows."
Yet if you use Microsoft's Lifecycle Policy search tool (
https://support.microsoft.com/en-us/lifecycle/search?alpha=Sync framework), only Framework 2.1 shows up. Now that does have support till 2021.
On topic:
I've found a Java implementation on GitHub called SyncFrameworkAndroid (
https://github.com/SelvinPL/SyncFrameworkAndroid) that could be used as a starting point for a wrapper. Looking through the code I've noticed two things: 1) looks like the Sync Framework uses URI's, meaning this could be implemented via okhttputils and 2) documentation on this seems to be scant (author complains) and doing some quick searches, this seems to be confirmed (the scantness of documentation on the URI approach to syncing).