There already is a three.js plugin, albeit 3rd party:
The only "issue" is there is no 3D view in the editor, which is fine in my opinion as C2 isn't really a 3D game maker.
I do agree there should be more first party support with C3 compared to C2. I don't expect a first party plugin (which would be nice) but I do hope they allow the Editor UI to be modified and have editor plugins that can add in a new window/panel. This way at the very least users can not only make a 3D game via a plugin, they can better modify the game through an editor plugin made to display a 3D editor window/panel.
Hopefully the news we receive over the next few weeks about the new features will be good.