Will Unity support Metal 2 which was introduced in MacOS High Sierra and iOS 11?

If so , which version of Unity Editor support this, 2017.1? 2017.2 or higher?

As far as the Unity roadmap goes, and it has Metal as a tag available, it won’t be available for some time, not until 2017.4 if even then.

https://unity3d.com/unity/roadmap

Adding to the response by @hexagonius - Metal 2 is not on the roadmap and as such you should not expect Unity to add support for it.