Wordpress doesn't have to do anything, when they people say MariaDB is a drop-in-replacement for MySQL they mean it. On the functionality front, except for details that only gearheads and MySQL DBAs care about you can view them as identical.
MariaDB certainly seems like the path of least resistance in this case.
Which means Monty has screwed everyone again. He should have let MySQL die in Oracle's cradle so the open source world could move over to a better database: PostgreSQL.