And in practice, that separation layer lead to objects tied together across COM boundaries, and severe memory leaks for any significant applications.

Yes, the Windows Script Host. But I don't believe two languages could very effectively talk to eachother, right? Couldn't they only really interact with the native code stuff (DOM etc.), i.e. the easy part?

It wasn't too difficult to add an interface to COM from a new language, that seemed the easiest way to call "out" to something else.