The thing about querying remote tables, especially when joining remote tables with local tables, is that the performance impact of the SQL coding tequnique is critical. I'm not sure that using synonymns to abstractly swap out a reference to a local table versus a remote table would result in the most efficient SQL, and it may often result in a very poor query performance. So even when the time comes to point that synonymn to a remote table on another instance, the developer may end up having to go back and re-code the structure of the SQL code anyhow. The usage of synonymns may actually obfuscate the underlying problem and make refactoring harder, because when reviewing the SQL code, it looks like only local tables are being referenced.