The supported version of the Sync framework ships with the product and any subsequent updates. Microsoft has explicitly made exceptions for products that ship with SharePoint such as AppFab.
What this means is that unless there is a specific note that updating a particular product that ships with SharePoint is supported, then it would be unsupported to install a newer version of the product. This has been explicitly true of the SQL Native Client, where only the version shipped (or updated) with the product is supported.
That said, for an absolute definitive answer, I'd strongly suggest you open a case with Microsoft Support. They will tell you what the supported parameters are. If they let you know that it is OK to updating the Sync framework, please post back here.