Happy to answer and sorry it took so long!
From time to time, we look at the logs and send emails to organizations that do not have paid plans and whose aggregate builds are more than 1,500 minutes in a given month. To date, we haven't had the need (or desire) to shut anyone down for going over. Most folks either upgrade or realize that they unintentionally left a webhook running on a project that builds constantly (which uses AWS resources that we still incur costs against!)
As an organization, CircleCI cares that users get value out of their CI system. If you are getting value and using us for work that matters to you, hopefully you'll consider our paid options (you will get more containers for concurrency AND parallelism, you'll get engineer support, and features like Insights!).
Finally - we do have plans to show linux minutes in-app in the future but it's not on the current quarter's roadmap.