Has anyone worked on a built-in CLI terminal [w/ drush]? What would make my experience with clients/end-users easier is if there was a self-contained GUI-like terminal that would be exclusive to their drupal 7 subsite in a multi-site configuration. This would allow them to be full-stack developers without the headache of managing *nix users? 

The only reference I could find was for Drupal 6 - https://drupal.org/project/terminal. 

In the meantime, the way I can think of manually achieving some of this is to write custom forms on a user dash (page--front.tpl.php) that would trigger drush calls on the server side for particular (custom) tasks. Maybe add some ajaxy for wiz-bang. 

Now granted, a lot of the customs tasks I can think of atm can be achieved via drupal modules - such as editing css, limiting access to module uploads, and even exposing features. It's just turning each one of those on/off for over 100+ sites is cumbersome, and so it'd be nice to leave it up to the end-user to manage their own site. 

Without paying Pantheon to do the same thing.
The upcoming Drush 7 now has drush core-cli which used the Boris shell