Unless you are actually using 5.6+-specific features, then mariadb is to all intents and purposes fully compatible.
Or, as the wikipedia article on mariadb puts its:
MariaDB version numbers follow the MySQL's numbering scheme up to version 5.5. Thus, MariaDB 5.5 offers all of the MySQL 5.5 features
Keep in mind, too, that mariadb's lead developer is Monty - mysql's original author.
Unless you are concerned about support for code you specifically wrote for mysql 5.6+, then I don't think there is a compelling reason for avoiding mariadb (beyond personal taste and possibly support options).
If you do need 5.6+ features, then I would suggest you check if your specific needs are supported (and possibly, assess the 'cost' of making some alterations).
Most things that 'require' mysql that I've run or installed, for some years now, seem to be entirely happy to use mariadb, and mariadb has an explicit intent to be a drop-in for the (now) Oracle MySQL.
You don't mention what concerns you have about the switch, but I would suggest you at least consider re-assessing your fears about MariaDB - all else aside, you may find it makes your (operations') life easier to use your chosen distro's default choices than needing to deal with integrating alternatives.