I don’t think this particular variant has been proposed…
This would be a long period event (perhaps even entire month). New energy type; monetization is by selling flasks, as usual, and perhaps some specific deals.
How it works — select your team to start with, and then select each of your heroes in the order you want them to appear. (Alternative, requiring much less coding/UX work- start with lowest power, increase as heroes die).
Gameplay — roughly normal, but when a hero dies, it’s replaced by the next hero you selected. Waves are successively more difficult; rough progression would be wave 1 = s1:1, 2 = s1:2, … but it’s algorithmic, so there’s no end. Boss levels every 10. Titan level (like S2 end or various s3 levels) every 50. Battle items refresh after boss/titans. You can pause between waves.
Each wave costs 1 energy. Maybe 5/day? Flasks for more.
Rewards — minor loot every wave, but more for boss levels. Much more for Titan levels. Probably never any rare ascension materials, or perhaps only a small chance after Titan levels. (Alternative, leaderboards with tiered loot based on end score/level, like many other events).
Yes, I know, yet another event, and one that may take a lot of time. And yes, it favors deep rosters. But that’s the nature of the game, and it’s what the devs clearly want.
And yes, resurrection heroes (MN, Alberich, etc) have no use as far as resurrection goes. Shrug.