I will soon release the next version of txtorcon with a ton of cool new features. This will be called 0.19.0. More details:
Going forward, versioning will switch to a "CalVer.org" variant. At one point, I thought of breaking a few now-regrettable APIs.
However, I will not do this.
The next version after 0.19.0 will be 17.x.y Changes in any existing APIs will be done by first introducing the new thing, deprecating the old thing and eventually removing the old thing. The new documentation's "programming guide" includes some notes on API stability. I have not to date broken/changed any existing API. Also at this point nothing is deprecated (but there are "preferred" APIs).
The onion services APIs *will* change for the 17.x release.
New code should follow the recommendations in the programming guide. Existing code will continue to work for the forseeable future.