I'm not for that tbh. Unless you make it entirely out of the game, like the black pit, its merely create a place where you can earn exp and items with minimal storytellings. Colliseum is the epitome of boring, Fedex questline and is kind of an excuses for lack of a better story. It's also boring because it can only be solved through combat, and not through discussing/ searching / sneaking / whatever creative option this kind of game can offer.
Fair enough. I guess the idea doesn't really cater to you however have you read and understood what I wrote clearly? Coz it's pretty clear you've just read the title and given your feedback. If the idea is implimented poorly I don't want it either.