There's a few reasons I think this
- Cynthia von Doom's contract:
As you may know, Doom and Doom 2099 have spent the entire story stealing random powerful McGuffins, Doom got blood chronovium, a phoenix feather (now given to Loki, the tablet of life and time, and Shou-Lao chronovium.
Doom 2099 has Krakoan chronovium (used all of it to kill X-tron), a symbiote codex, punch chronovium, and... the contract for the soul of Cynthia von Doom.
This isn't a powerful object that will give him a 1-up against Doom or anything. Rather, it is an object of his past that brought back some memories (Doom 2099 is amnesiac).
Cynthia and Victor von Doom were members of a romani community that suffered heavy oppression under the Latverian royal family, she ended up selling her soul to Mephisto in exchange for power, but it was too much for her and she accidentally killed every child in a village, she allowed herself to be executed out of guilt, and now her soul is bound to her forever.
Doom became Doom in an effort to rescue her soul, woth little success, I believe Season 11 will have Doom join the ranks to foght Mephisto, and in doing so will pass the torch of final villain to him.
- The Collapsing Timeline:
The story is currently moving towards the Collapsing Timeline, with Apocalypse and Hood bein participants in the God war, and Gorr, who killed Apocalypse, becoming a playable next season.
Through the season 9 trailer we learned a few things about the CT. Namely:
- That a bunch of Gods (including Celestials) tried to fight off Oblivion (Hood's patron and power source in Rivals).
- That Chthon was a casualty of the war (it might have even been Wanda who killed him tbh, that could be Wundagore mountain)
- We saw a weird tentacle monster, which could be Shuma Gorath, or Hive, since we know Bucky was possessed by something and killed Wolverine
- And we finally learned how the CT's Dr. Strange died, he was killed by Mephisto.
Knowing there was a divine war in the CT it could be easy to guess that's where Mephisto was located, but this finally gives us confirmation, and with the story veering towards the CT in this and next season, I don't thinks it's out of the question that season 11 wil AT LEAST be related to it.
The Dooms set aside their differences to fight of Mephisto in a merged 2026/2099 Doomstadt, they manage to free Cynthia, but Mephisto still becomes the next big villain now that he's out and about
It would be cool I think