Thanks for the suggestion. I agree that this would be useful. Please note though that if you choose to include all test cases in a test run, new test cases are also automatically added to active runs. I’m not sure if this is practical in your case, but it’s usually the easiest way to ensure that all test cases are included.
Closed test runs are of course not affected by new test cases, so you wouldn’t need to worry about your archived runs.
PS: We also have a custom report that shows the results for all test cases of a suite (or even project) for all active test runs. This might be a good way to track this in the meantime. The report is a custom report that directly accesses TestRail’s database. Feel free to email us if this would be of interest to you.