That's true—the actual IME is much more flexible than this. My point is more that this isn't really anything new. It's a fairly common way to Romanize Japanese

That's true—the actual IME is much more flexible than this. My point is more that this isn't really anything new. It's a fairly common way to Romanize Japanese in practice, even though it doesn't strictly follow Hepburn or Nihon-shiki. In fact, this style seems to be more widely used in the Western "fandom" world—on platforms like AniDB, Danbooru, and others—than the two "official" systems.