Oh, I absolutely agree with you that “meaning of the oneway tag should not change”; in the same meaning that I agree that there “should not be wars”.
Sadly, reality in both cases is that it does (often) happen, regardless of our wishes and best efforts.
Thus, taking into account unavoidable future where our (shared) wishes will be disregarded by many; some pragmatic solution for handling that problem of tagging amiguity in more usable way (i.e. making the tagging non-ambiguous) should be devised (thus: oneway:foot and similar proposals)
(but hey, if you have some magical way to make every mapper becoming instantaneously enlightened and starting tagging as it should be done, which does not involve OSM becoming dictatorship and ruling with iron fist; I’m all ears!)
Otherwise it will introduce errors when mappers refine footways with steps or vise versa.
Surely, mappers “refining footways” should look at the things that they are modifying, right? Also, what exact problem for such refining do you forsee that using oneway:foot=* will not make better (as opposed to using only oneway=*)