Hi devs,
At MariaDB developers meetup, there was a discussion about enabling unix socket authentiation [0] for the root user by default for new installs of MariaDB (this is currently already enabled in Debian testing and in Ubuntu)
Basically this means there is no password for the root user, which is possibly a problem using phpmyadmin out of the box on new installs with MariaDB.
It is of course possible to create another user with a password, even for root, using shell as root (or with sudo).