As far as I ever read, the term "internal" was a fairly modern thing (relative to the age of the Chinese arts in question) coined by Sun Lu Tang or at least someone of around his time, so it is probably a stretch to call it ancient. I think it's just terribly non-descriptive, beyond being a loaded term.
Someone handed me a model of what the human body might be capable of which more or less went: "Imagine the majority of all voluntary muscles in your body simultaneously contracting to the fullest of their abilities in a single direction and then instantaneously relaxing." That sure as hell sounded a lot more compelling to me than "ki" or "chi".
Hmm, the human body is such a complex instrument (as are almost all life-forms, and we are naturally largely similar to the others) that generations of scientists and doctors have specialized in attempting to understand and deal with even so-called minor components of it. Yes somehow a vastly simplified view of any aspect is going to give on insight into all the complexities, with no further effort needed? I don't buy it.
So, while certain basics might be fairly easy to convey to someone and get them started on doing their own research (the "ease" of such conveyance should not detract from the difficulty of getting such insight on one's own), such an elementary beginning (analogous to perhaps the letter "A") does not allow such a beginner to even see what might be possible at the letter "Z", let alone do that kind of stuff, not to even speak of putting the various components together into a synthesis to do other vastly more complex and sophisticated stuff. A simple summary might be: If your body is not ready for "B", work at "A" until it is, and progress in understanding from there on that practical basis.