Don't know if this has been suggested or not, as I didn't look nor have the want to look.
Anyway, as a friend and I were doing our The King of Ashes run, specifically the part where like ten or so waves of Slag Walkers spawn, and we thought it would be neat to have endless waves spawn (for heat and crowns at the time). Well then the thought hit me, why not make use of King Krogmo's Coliseum and add a survival game to it. Endless waves of monster spawning, each wave gets harder, etc.. Ya' know what I'm on about here.
No one plays Blast Network anymore, and don't get me started on Lockdown (lol). KKC needs a Zombie Survival game!
i would like it, only they would have to increase the difficulty because we already do it normally when we have to face an arena or a danger room.