As a native speaker, I've never heard about this "IME". After some research, turns out it's a layout (see crbug.com/890138 on how the term "IME" is currently overloaded). I think a vast majority, if not all, Vietnamese-speaking users do *not* know about it. We should consider retiring it. 

I reckon it's supposed to be a "standard". TCVN = "Tiêu Chuẩn Việt Nam" lit. "Vietnamese Standards". However, it must've never made its way into practice. I can only find this Wikipedia page (in Vietnamese): https://vi.wikipedia.org/wiki/TCVN_6064:1995. Microsoft once added a similar layout to their OS, but never used in practice. Don't think there's physical keyboards made with this layout either.

Vietnamese typing has always been done via an IME on a Latin layout. Nowadays it's most commonly Telex and VNI on both virtual and physical keyboards, and to a much lesser extent VIQR on physical keyboards. IME choice is based on their characteristics, as well as personal and regional prefs.