when stable haxe 4 out ?
When haxe 4 is ready / when the backlog is empty, I guess (https://github.com/HaxeFoundation/haxe/milestone/10, which has a deadline set on May 01, 2019).
Maybe someone from the core team could give you a more accurate answer, but I’m not sure they can be really precise either.
While there is no date set for it, the current priority is to finish Haxe 4.
Also Haxe preview aren’t especially less stables than a release, so if you want to test some of the new features you can give haxe4-preview4 a try.