As for my own actual thoughts, having spent a couple of weeks thinking about it, and sifting through the evidence (that I can find) trying to apply common-sense packs etc; I've come up with what I would actually like to see (rather than a bunch of "not that"s)
I would drop the tackle height to armpit / nipple line, but I'd make it that the tackler's head needs to be below that target line OR the tackler's target line needs to be higher than the ball carrier's head.
I'd then encourage (or make law if taken up by WR) that shirt-companies put... something... at that line to make it more easily visible for refs.
The point is to get 1 players head away from the heads and shoulders of other players.
I don't really care which is higher, as long as they're not in the same place (as a trial, at least - but that trial needs to be at least 1 full season).
This still allows a buffer zone for misjudgements, between the armpit, and the bony top of the shoulder - about 3" (NB this is supposition. As far as I'm aware, the research hasn't differentiated between the bony top of the shoulder, and the meaty outside of the shoulder.)
I think heads are easier to see than shoulders at point of contact, especially at lower levels with no replays and no touch judges interventions.
I'm happy with "encouraging ball barriers not to dip into contact" - depending on the final wording and interpretations.
Bracing for impact should be fine; but not the "lunge & present shoulder" we see from some of the bigger wingers to bounce tacklers off them. The point here for me should be about showing the tackler where they can hit you, and then not deliberately changing that - height wise.