I believe the change you were proposing (althouth you seem to be leaning away from it now) was to add this to the AoO rules:
Making an AoO while in a threatened square, provokes an AoO against yourself.
This seems to fit with the language of the origninal rules, but I can see the problems with it (as already mentioned throughout the thread).
But what if it was stated this way:
Making an AoO while in a threatened square, against opponents other than those which already threatened you, provokes AoO's from those opponents that already threatened you. You do not provoke an AoO from the opponent that initially provoked your AoO, even if they currently threaten you. The AoO's you provoke from opponents that threaten you, do not also provoke AoO's.
In other words, if you're in a threatened square, and an opponent that threatened you does something to provoke an AoO, you can attack with no adverse repercussions (Orc B in the OP - this is different than what the OP proposed - I don't think that Orc C should get an AoO against Fighter A). But, if you make an AoO against someone that didn't already threaten you (such as an opponent passing through a square you threaten - call him Orc D - or Bull Rushing/Charging/etc into you...but they didn't previously threaten you) then opponents that already threaten you may make AoO's against you. These AoO's do not also generate an AoO from you (so,
no infinite AoO loop...).
This works for me. I don't see any extra problems from this...unless I'm missing something...though it does add some extra complication to the rules. I don't mind that extra complication, and if your players like the facing rules, they probably won't mind either. However, I don't see the argument about there being more things to track...? But, there is some added complication to the rules.
I actually use something like this in my own games. But I've done it from the approach of adding an "Engaged" condition. "Engaged" is defined as:
any time you have attacked an opponent or been attacked by an opponent, excluding AoO's, you are considered "Engaged" with the target(s).
This leads to:
Once you are "Engaged" with an opponent(s) you cannot make an AoO against an opponent you are not engaged with, without provoking an AoO yourself.
But, after reading this thread, I think I better like the above addition to the rule. (The one in the second quote box.)