Before opening an issue:
When asking general "how to" questions:
When reporting a bug, include:
When suggesting a feature, include:
When everything here : https://github.com/twbs/bootstrap/issues?q=is%3Aopen+is%3Aissue+milestone%3Av4.0.0-beta will be closed/resolved
Bootstrap 4 is currently at Alpha 6 and is currently being worked on. It's not even at Beta 1 yet. You can see what's being done to move towards Beta 1 here: https://github.com/twbs/bootstrap/projects/3
As you can see, there's still a lot to be done. According to the v4 Alpha page, Bootstrap v4 is a major rewrite of nearly the entire project. (from here: https://v4-alpha.getbootstrap.com/migration/)
Basically, when everything that needs to be done is completed.
Also look at mdo's response to this very question from yesterday:
Most helpful comment
Also look at mdo's response to this very question from yesterday:
https://news.ycombinator.com/item?id=14446066