Are you saying that there would be two athletics checks per round, one on each participant's turn? I thought the grapple was resolved with the first to act and the other guy(s) participated in that same full action check.
Why would fighting a grapple check be conducted any differently to any other combat action? All it does is limit the choices available to you.
It shouldn't be conducted any differently than any other combat action. If an orc hits you with its sword, you don't get a separate dodge roll on your turn. Likewise, if you lose the full-action opposed Athletics check in a grapple, you don't get a separate one on your turn. Combat actions are atomic and uninterruptable except for a few actions (Ready, Parry) that are clearly called out in their descriptions as to how they interrupt.
Note that I'm not referring to the initial check as defender isn't under the limitations of the grapple rules until after he fails it. By the grapple rules, the only non-free action a participant in a grapple can take is a full-action opposed Athletics check. That's what limits your choices.
That's an interesting read, though as Mr. A's said it would be a significant departure from "the norm" of combat/init order/action economy.
On the contrary, I think it's the standard way. No other condition (held) gives you multiple attempts to break it every round. Outside of a grapple, you can participate in one full-action per round. Why should it be different inside of a grapple?
I look at it as the involuntary version of becoming a mounted character.

Once mounted, each character no longer acts on his initiative but rather they act as one. Likewise, a grapple is kind of a collective where everyone has a limited set of actions.
Otherwise you're allowing the participants in the grapple to take multiple full round actions in a single round in addition to the delay silliness mentioned earlier. Refusing to make the grapple check shouldn't stop your opponent from pinning you, it should assure it.
Forcing the opponent to sacrifice all his actions to participate in your check sounds like a pretty hefty benefit, but it might not be bearly as bad as it sounds in practice.
For most creatures it's the only point of a grapple. Unless you're a giant snake, you're probably grappling to prevent your opponent from taking his usual effective actions and in return you give up yours. Rolling multiple times per round shortens the grapple and makes it a less effective hold.Yes, you can pin someone quicker, but that's not really the point of a grapple.
I don't know that my reading is the intended reading but it seems (to me

) to be reasonable. You have all of the same options but the single check per round means two equals end up grappling for more than a single round. And it avoids the go-limp defense.