I don't have a solution for you other than to suggest that you may be able to synchronize data to another platform using external 3rd party database tools.
For custom features you can write your own code and use any database platform you want but for built in things we support using either MS SQL, SQL CE, MySql, PostgreSql, Firebird, or SQLite. But you can only choose one, you can't put some data in one platform and other data in another platform.