I suppose it's licensed under a non open source license until it's released to the public. If so, you can prosecute such individuals who break the license.
True, although just removing a couple of words from the MIT license would still be a very attractive and easy to use license. Examples of words you might remove: "sell" and "sublicense".
So as a user, you can start some work based on the insider version and be confident that you will be able to release your work even if the insider version never goes public for some reason, instead of relying on a promise that the code will be released in an open source license.