Apparently in the chat on Friday Christopher stated that all the Heroes in Oblivaeon would be people we had seen before. I think it's basically confirmed that one will be Lillian Corvus and another will be Baron Blade, and that none of them are Scions or Proletariat. That still leaves...quite a lot of people.
Anyway, I would like to put forward my guess, which is the ape from Quando? Ahora! because seriously, great ape.
I think Cold War is a good possibility. I don't have the quote in front of me but I believe they said he was not a promo in the first Q&A.
I see Fright Train as a possibility since much like the incap side of Baron Blade it specifically states villain turn. All of the other three villains from that set don't specify villain turn.
But in the first Q&A, I am pretty sure he also said none of the alternate reality heroes would be getting their own decks. Instead, they'd be showing up in other ways. (There's been speculation that maybe they are going to be in envorinment decks.)
My bet is Harpy, Blade, Fright Train, and Ermine. And I'd say the last was Proletariat, but that's a confirmed "No", right? And Deadline has lost his tech, so he probably isn't a good option. Have to think about that last one...
I'm actually wondering if the grown-up Dreamer might become a hero deck. It's not clear how essential Project Cocoon is to the creation of the Visionary; without it, Vanessa might grow up to be an entirely different hero (or villain post-Dreamer). It's clear that she's powerful.
Here's one idea that hasn't been mentioned: La Commodora. After all, if the theme is "villains on the side of heroes", Future Good Capitan would certainly qualify.
I'm hoping for that Setback/Legacy combo and maybe Lucky Strike, the Setback from Quondo? Ahora!
My hopes and dreams are on decks consisting of multiple crazy alts of characters we already know who are fighting together in a single Sentinels-style deck. That fulfills the statement that the alts don't get decks of their own and the statement that we'll be seeing them in other ways, while also fulfilling my heart's desire.
Tony Taurus. What was he doing in the Coloseum after all?
I am hoping for a kraken deck. After all, why wouldn’t the environments fight back too.
Every card is a target with keyword "TENTACLE."
That'd combo nicely with Super Scientific Tachyon.
Each time a card named Tentacle is destroyed, reveal cards from the top of deck until two cards named Tentacle are revealed.
I like Spiff's idea. And I think that we may see a lot of decks that are neither heroes, villains or environments in the "traditional" sense - like a deck of allies, or a deck of quests…
I'd consider Citizen Dawn for a hero deck. She'd probably try first to ally with OblivAeon, or use him/it, but once she understands that he/it is a danger for her citizens, she won't hesitate allying temporarily with her former ennemies. Also, it's good public relations.
And if OblivAeon wins, she probably has an Ark already built to leave the planet and go build a new civilization somewhere else 
Yeah... I think that we'll be seeing Dawn again RSN.
While I would like seeing Spiff's suggestion, those styles of heroes just take such a beating from AoE damage. I mean, for The Sentinels (and a certain Cauldron promo), it is a drawback built into the deck, sure, but it is offset by the amount of healing that deck has. I don't know if I would enjoy another deck of too similar a gimmick.
Maybe its just me, but I hate when everyone else takes 2 damage from an attack and my poor Sentinels team takes 8.
The Ennead. So you can play out Ra's final charge against OblivAeon.
Just because there will be no Proletariat hero doesn't mean the man behind the mask won't show up as a hero. We've seen this tricky wording before when it was stated there will never be a Matriarch hero deck.
Except that Proletariat still goes by that name in Tactics. So I rate it as unlikely.