You said: “It would be nice if a common posture was enforced for all dioceses. What would, IMHO, be even nicer, is that all the congregation abided by this common posture.”
Realistically, that’s never going to happen. The old lady with the bad knees is not going to do the same thing as the guy in the wheelchair, the ablebodied person, or the person who rolls in every week on a glorified motorized stretcher.
Also, the Church has always encouraged legitimate variances in local custom, just as it has never stamped out the various Rites in favor of just Latin Rite Catholicism. What has been judged as holy and fitting continues to be holy and fitting. Being too rigid on these points risks offending the Holy Spirit, who promulgated these various expressions of the one Mass.
I went to an Orthodox Jewish shul (synagogue) once. They had a very nice concern for their liturgical postures, yes. But they also had a congregation full of people whose families had come from all different places originally, and many of these places had had little idiosyncrasies in prayer postures and such. Since many of these towns were emptied of Jews by the Holocaust, most shuls apparently permit Jews to pray however they were taught, lest any of these legitimate customs die out and the Nazis win. So people got up and sat down, or bent and rocked, or did other things at what seemed random intervals to me; but it was clear that each of them was doing that thing at an exact time in an exact way for an exact reason. If you’d asked me beforehand, I would have thought it would have been disruptive. As it happened, it didn’t bother me at all. Everybody was working hard at worshipping God and being obedient; the exact way of doing it wasn’t as important as I might have thought.
And that’s how I feel about people coming back from Communion. I don’t care if they stand or kneel, as long as I can kneel (or stand) as I was taught. (And frankly, standing up for ten minutes in your pew is too much of a workout for me. I’m glad my bishop doesn’t go with that!)
Of course, my mother would poke me if I paid any attention whatsoever to what was going on after Communion, so usually I still keep my eyes shut just to be safe.