Clockworks Survival is my idea or a Endless survival, This can be a prestige Mission or a normal mission, there can be endless waves that get harder each time, and at the end depending how far you get, you get a spin for items like, New Costumes or Armour, Crowns, Energy, Or Keys and lock boxes and special materials. Also there could be a boss for each 10 or 5 waves. Also you can create turrets and summon Mecha Knights or Recon knights. and there could up to 2 Players.
This has been suggested before and would not be a bad addition to having arena base tournaments to see which player got the farthest in waves. But i think the devs want to emphasize players living through conflicts. So i think, there should be an intermission after every 5 waves where players can choose to quit but if they go further they would get better loot like the Christmas grinchlin event. Well this is the most systems used in other games like dragon nest or warframe.