While Doomsday appears that it is going to be a great movie and I'm looking forward to it, I feel like a prison break / villain team up would have also been a good avenue to approach. And yes I know that was the plot of Avengers Earth's Mightest Heroes, it would have been dope to see it in the big screen.
The plot could have centered around Zeke Stain aka Ironmonger 2 is contacted somehow by the leader and come up with a plan to release all the captured villains like whiplash, mysterio, Abomination, graviton, a skrull who later becomes a super skrull, lead by Baron Zemo and joined by Enchantress and Scroge from Asgard.
The Leader and Zeke create a Gamma Bomb, use Graviton and Mysterio as a distraction...
That doesnt have to be the plot but I think It would be cooler than constant coming up with different villains and killing them off... soon you will either have to draw from obscure characters, create new characters or use variants which will probably be played out after Doomsday. Even bringing back Kang won't be as compelling after Doomsday. Im curious is this the end of the MCU or how will you go forward after Doomsday?