We currently have unity, and unity5 as tags to differentiate general unity questions from questions about specific features to that unity version.
That's not exactly the case.
Taking a look at the page for unity tag synonyms, you'll see
unity5. This means that unity and unity5 represent the same thing, with the "front face" being
It's been discussed and decided the in the past that there was little value to add a tag for a specific increment of the engine. Like with the c++11🔗 tag that we had, users tend to tag their question with everything they think is valid. Letting users tag a question with
unity-2017 that is not specifically about the features that are exclusive to that version will end up polluting the new tag anyway.
Also, the feature you're mentioning seems to have been implemented in Unity 2017.2. To be perfectly consistent, we'd need a tag for each release of Unity in order to cover the new features. I don't think it's a good idea as we'll end up with a lot more of what I've described before. What if you need a feature from Unity 2017.2 and one from Unity 2018.1?
We've also decided in the past to convert unity-related tags to being synonym of
unity. Maybe the concept of tilemap in Unity 2017.2 is so different than what the basics of tilemap are that we'd need a
unity-tilemap tag. But then again, we'd need a watchdog for that tag, able to distinguish if the question is about using the feature of the engine or not.
An alternative approach is to use the search.