Personally I'd love to see something more like FFVII's Battle Arena which was also a part of Gold Saucer in that game and thus would be totally appropriate here! That one was basically see how long you last, and so just going hoping to tank and spank would quickly end in failure, due to the accumulating handicaps given to you with each successive battle you win, but the longer you lasted, the greater the rewards.

It would thus require a certain amount of finesse as well as luck rather than simply going in at level cap with your best ilevel gear and weapon, because oh dear, you now have Weapon Broken handicap and your weapon is now at 0% weapon condition (to use an example). It would soon bring many so-called 'elite' players down to size I'm sure.

Of course it would require a lot of balancing to compensate for different classes, but I'm sure it would be doable (no different to say THM/BLM having to do solo class quest fights). I'd love to see this added.