Three packages has been upgraded in -Current (and some of them are also in stable releases back to Slackware 12.2). They are hplip, mysql, and php. All of them are now upgraded to the latest version to bring improvements and also security update (only for MySQL).
Pat notified the user that this upgrade may possibly introduce incompatibilities with previous package, but i didn't see any changes in the Release Notes, except that SHOW AUTHORS and SHOW CONTRIBUTORS are now deprecated and also released lock of unmatched rows on a DML statement.
While several other Linux distributions have proposed to migrate to MariaDB instead of using Oracle's MySQL, Slackware (for now) do not have plans to migrate to MariaDB as far as i can see. It works well so far and if there's a problem in the future, Pat will make a decision based on the real situation, not based on assumption that Oracle will make MySQL have lower quality after the acquisition from Sun Microsystem.