One of the major issues is that if you type
whoami at the console, you'll realize you're logged into the shell as www-data. We are working very hard not to introduce vulnerabilities that would allow a non-master user to gain root control of the box -- giving www-data full sudo access would certainly fit that bill.
I am not entirely certain if it is possible to run a web script that is displayed by apache by any user other than www-data...
However, I just tested this out: Any of the commands in visudo that are granted to www-data with nopasswd can be run from the webconsole, i.e systemctl restart rtorrent@user, etc.