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OK most of my question, it seems, is reluctantly answered by a VUE team member here: https://github.com/vuejs-templates/webpack-simple/issues/29
The author of the question writes that he was downvoted on StackOverflow for the question which, as it turns out, is quite popular and needed.
From the answer I understand why h was chosen and what it replaces, why $mount was chosen and what it replaces.
Still not sure about the render and the extend. But that’s a separate question.
Source:stackexchange.com