I mean, there would be sex with at least one of the participants. Be it as a reward for completing the trial. Since implementing just combat encounters without sex by fans is not allowed.
I assume by 'fans' you mean non-Staff writers, and not 'fans' in the context of arena fans. I believe non-Staff need to submit a sex scene with an existing NPC before other projects, but that doesn't mean every submission must involve sex, especially not every combat encounter. It wouldn't make sense. There'd by no TF-items (without somehow having every one make you so horny you start jacking off), or any combat encounter like wolves or animals or creatures or elementals. It wouldn't be reasonable to expect someone who designs an amazing encounter, creature, or combat design to have to force a bestiality scene (which wouldn't even be allowed) or have to do a party check and add in a scene with any potential random party members to start a sex scene
"Good job beating those serpents," Arona says. "Speaking of long green snakes...." or just suddenly have a random woodsman show up after you defeat the wandering Jabberwocky and be like,
"Now there's meat for the village! Let's celebrate with sex!" just to tick a checkbox when it narratively isn't needed or would be reasonable.
I am certain if you have a cool arena gladiator or encounter (like a naval battlescene), and it would fit, they would consider it, and not require you to chain down and butt-fuck all the losers (I mean... unless you wanted to write it). Or at least ask. There's plenty of sex in Khor'minos, they don't have to shoehorn it in where it isn't needed. All the runners in Rina's competition didn't get forced into an orgy after losing.