Right, happy to report that install #mysql 8.0.11 was pretty painless on #UbuntuMATE #Bionic
Slightly less so on #Kubuntu #Bionic Had to purge the mysql-server and mysql-community-server packages and then install them again.
Or, put another way, I had to remove the older config files, and the database files before installing the new version of mysql.
And finally, I got a prompt to set up a root password (:*
And I've given myself full privileges, if I ever need a database.