and I think I might add the entering threatened squares granting an AoO BUT if the attacker does that they cannot move that round, unless they have spring attack (yay for spring attack!)
I think, if such a rule was added, that there'd need to be a possibility of a hole opening up in the foe's defenses.
I picture two combatants, swords out, facing each other, moving around each other, looking for that right moment to strike.
The question is how to do this mechanically. On the first round, when the foe is flat-footed, that is definitely and opening.
But, what about on later rounds? It seems like there could be some kind of check (Appraise?) that allows a character to find the best moment to strike.
This would be a neat mechanic (thinking outloud here): Two combatants square off, neither willing to jump in and risk the AoO from the other.
As a free action (or maybe it should be a standard or a move action?), a character rolls an Appraise check (Appraise to best guess when to enter into combat). His foe does not yet roll his Sense Motive check in answer to the Appraise roll. Therefore the player must decide, on the strength of his roll, without yet seeing what his enemy rolls in response, whether to keep circling his enemy or dash in and make an attack.
Once the player decides to attack, the foe immediatly rolls Sense Motive against the players Appraise throw. If the foe wins, he still gets his AoO. If the payer wins, the character has successfully found a hole in his opponent's defenses and exploits it.
That's kinda neat, huh? Maybe the actual skills uses should change, but I like the uncertain action. Sounds fun.