moot point

An issue that is subject to, or open for, discussion or debate, to which no satisfactory answer is found; originally, one to be definitively determined by an assembly of the people.

An issue regarded as potentially debatable, but no longer practically applicable. Although the idea may still be worth debating and exploring academically, and such discussion may be useful for addressing similar issues in the future, the idea has been rendered irrelevant for the present issue.