Please take this in consideration as features request:
1) Nginx as alternative for webser to Apache. 1') Apache 2.4 instead of 2.2
2) Nginx and Varnish as proxy servers in front of web servers.
3) HHVM or PHP-FPM when Nginx as alternative for PHP
4) MariaDB and Percona as alternatives for MySQL
For the moment I am using the default installation script, but replacing mysql-server-server and mysql-server-client with percona's. I have a better performance using Percona.
In Magento using Apache + PHP5.5 + MySQL against Nginx + HHVM + Percona I get 3 times more performance when using Nginx.
In case you cannot add these to Webmin/Virtualmin, please make tutorials for installing without creating any trouble, you know better than anyone your software.