Your example provides an interesting problem for the ISO standard, "how do I get it to describe what my mid-tones will do in a print?" In a simplified sense, it can't, the question the ISO standard and other shadow point methods answer is just "what the reasonable lower limit?" We still have to figure out how the rest of the film behaves.
If the "print reference point" is the "metering point" and that was simply a density of .4 or .45, something appropriate, we might talk about film characteristics differently. TX might still get a 400 rating and TXP might get 200, so what, .4 may very well be a better predictor of print results.