With a straight exposure of our APIs to GDScript (or through native script) it should be dead simple to reproduce what you see in the video. All our runtimes across all languages (Java, C#, Lua, ActionScript, C, C++, TypeScript) work exactly the same. The code of that demo project would translate 1:1 to GDScript (with some changes to make the API a bit more idiomatic).
You can follow this issue which I'll update once work starts and progresses [godot] Add support for Godot Engine · #728