Hello Brian,
It's always good to know there is support for tabling all called hands at the showdown. Back in the old days...30 years ago...some cardrooms in Vegas did go back to the earlier betting rounds when the late rounds were checked. I believe it created too many problems, and delay's, so the last round is the most practical to consider. As far as "order of showdown" there are times when it is completely normal for a player to turn their cards out of sequence. The best example would be a player holding an exclusive nut hand. Why delay the outcome?
I agree with Ken about the "last aggressor." I always thought that a slight change in wording could further clarify this rule. For some reason, many misunderstood the last bettor or last to raise. I've always explained it to my students like this: The player who initiated the final bet or raise on the last round. All I can say is, everyone understood.
I also instruct my dealers to address the proper player to show at the showdown.