DB-Engines.com (http://db-engines.com/en/ranking/relational+dbms) ranks MySQL as the #2 most popular relational database after Oracle. MySQL is continuing to grow and gain market share. MySQL 5.6 and 5.7 show the database server is continuing to add significant new functionality in each release. MySQL is extremely fast and scalable. MySQL cluster can also perform well against the fastest transactional systems in the world.
Hadoop is growing extremely fast in the big data side of the world. MySQL is the relational database of choice for the metadata repositories in the Hadoop platform.
Point is, MySQL continues to grow in market share and popularity. MySQL is a good database to have as a skill set moving forward.