First of all this game mode is a really awesome idea and I already wished for something like this for the first game.

But sadly this mode is very limited in it's possibilities and options so at the moment i'ts more of a demo than a fully and complex demo.

My wishes for a big future content update for the arena would be:

-Completely custom characters with their own skill and attribute builds.

-A way to have a complete individualised equiptment for my characters. Right now arena characters only have white equipment without any special stats and effects on it. That leaves out so much potential of the game's system.
The game offers so much complexity and options to tune a character with equipment, the runes, echantments and so on. It would be a blast to create tons of different character equipment builds and let them fight against each other.

-An option to save and export my created characters to share them with friends and the community.

-A way similar to the GM mode to create custom arena maps.

I hope Larian will give this game mode more attention in the future and maybe add some of my ideas to it.
There is nothing better to have some awesome PvP battles with friends in in a complex and deep RPG system like Divinity.