How to track what has (or hasn't) been "featurized" in the UI?
Try using the configuration module along with Drush. It writes the configurations into files which you can manage using GIT. 

You run drush config-export –all on your dev and push your code with the config using GIT. Then you pull the changes on your prod server and run drush config-sync. It takes the config from the text files and puts them into the database making the changes live on the site.

Here is a nice article which explains this - https://shanetully.com/2014/04/drupal-and-the-holy-grail-of-workflows/