Both the downloader and transformer have been extensively tested with real-world use and are now considered stable enough to warrant a version tag.
SE still has many ongoing initiatives that can and will break parts of the system. An upcoming rate limit change may break the downloader, and future versions of the data dump may have further changes that the system does not work well with - but the downloader works and should be difficult to break, and that's the critical part.
It may, and likely will break at some point in the near future, but that's a future us problem. By my estimates, assuming I haven't gotten my months mixed up, we'll find out in 15-20 days.
Long live the data dump