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Re:TypeScript 1.4 sneak peek: union types, type guards, and ... by ahmelsayed on Wednesday November 19, 2014 @02:11PM (#8631977)
that's not really the actual timeline. here is the pull request for adding union types. https://github.com/Microsoft/TypeScript/pull/824

I believe all 3 teams, TypeScript, Flow, and AtScript, are working together for few things as is.

Re:TypeScript 1.4 sneak peek: union types, type guards, and ... by inglor on Wednesday November 19, 2014 @03:34PM (#8632444)
AtScript are working with TypeScript and supersets it.

If you look at that TypeScipr PR, you see it closes an issue and they reference (2 months ago) Flow there.