I personally do not love arena's for fighting ...
But after all you ideas are not stupid at all.

And maybe with turn based combat an arena fight is more enjoyable for me that a real time fight in a arena, who knows ?
But to be honest: I only want such arena and fights against eachother
IF this can be implemented (in some way) in the story of D:OS .
Not just "fight because of fighting", how funny the TB combat may be, but for me a "No no no no no ... !"