Counting future decks (from OblivAeon and the mini-expansions), there are (if I've counted right) 29 hero variants and one villain variant yet to be released in the video game.
I thought I'd see if anyone had ideas (that they were allowed to share) about what the unlock requirements might end up being for some of these remaining variants. Obviously, I don't expect to get any of these 100% right - most, if not all, of them will have additional requirements about what cards must have been played, or must be in play, or must not be in play, or character order, or... you get it. This is more a starting point to see what people think might happen. And for some of them, without knowing their decks, it's really hard to come up with things they might have to do.
Variants tagged "OblivAeon KS" were unlocked for the physical game as part of the OblivAeon Kickstarter, and Handelabra has said multiple times that they won't release those until OblivAeon itself has shipped to its Kickstarter backers (Omnitron-U being a one-off for their Season 2 Kickstarter).
Villain:
Unstable Kismet - Defeat standard Kismet. Then, while fighting in the Block, have n Prison Riots played during one game.
Already-released heroes:
Dark Conductor AA - Lose to Biomancer with regular (or PW) Argent Adept on the team. Then, ???
Fused CC (OblivAeon KS) - Defeat standard Infinitor, then defeat Heroic Infinitor. Captain Cosmic must be the first hero in (at least one of the two, maybe both).
Best of Times Chrono-Ranger - Defeat La Capitan in single-villain mode, then defeat La Capitan in team mode in the Final Wasteland. Chrono-Ranger must participate in both battles, must not be incapacitated in either, and may need to deal the final damage to La Capitan in the second game. (La Comodora may be required, which would push this back to after OblivAeon's digital release, but there are few enough variants not waiting on OblivAeon to ship that I'd think they'd want to get this one out sooner rather than later.)
Fugue State Parse (OblivAeon KS) - Omnitron and Progeny are probably both involved somehow.
Setting Sun Ra (OblivAeon KS) - OblivAeon, The Ennead, Fanatic, Fort Adamant, and (the Tomb of) Anubis all play roles in the story comic this relates to. Not being a playtester, I'm unclear on exactly how OblivAeon's play mode is going to work, but I seem to recall hearing that it uses multiple environments and might allow for villainous characters to contribute in some way.
Extremist Sky-Scraper (OblivAeon KS) - From the story excerpt provided, it would make sense to have Luminary and possibly Tachyon involved in some way.
Unleashed Visionary (OblivAeon KS) - Have the Argent Adept heal Dark Visionary for x amount of HP (in a single game? A single burst?).
Freedom Five: (OblivAeon KS) - All quotes in this section are from the KS update that revealed these variants.
F5 Legacy - The Freedom Five have "seen the worst of time and the worst of space". This would seem to suggest Time Cataclysm and/or the Nexus of the Void.
F5 Bunker - "Lt. Tyler Vance has been pulled in multiple directions lately. The U.S. military was revealed to be capturing and training/reprogramming super-powered individuals AND stocking items of great power. Lt. Vance’s duty to his superior officers were running in direct conflict with his duty to his team." More Chokepoint goodness?
F5 Tachyon - ??? I got nothing.
F5 Wraith - The mask on this costume kinda reminds me of Spite, which suggests to me that fighting him might be a requirement (ugh).
F5 AZ - "If he hadn’t been so abysmally bored, he would have just stayed in the cryo-chamber and goofed around on the internet for the rest of his frigid life." Have Cryo Chamber in play at the same time Freedom Tower's card Frost's Cryo Chamber is also active?
Xtreme Prime Wardens: (OblivAeon KS) - Each member of the team will likely have the first step or two be essentially the same: "Lose to Progeny, then defeat Biomancer (possibly in the Ruins of Atlantis), then..."
XPW AA - Have (specific variant of?) AA be incapacitated by damage dealt by Ruin.
XPW CC - ???
XPW Fanatic - Probably something to do with the Court of Blood and/or Apostate. Jeremy has mentioned that Christopher wanted PW Fanatic's unlock to involve the CoB, but Handelabra shot that down because it meant they wouldn't be able to release hers at the same time as the other PWs; I can't imagine that's not going to be involved in XPW.
XPW Haka - PW Haka is incapacitated in Magmaria.
XPW Tempest - ???
Mini-Pack 4 Heroes:
Benchmark: Supply and Demand - ???
Action Hero Stuntman - ???
Void Guard (Mini-Pack 5) Heroes: - I wouldn't be surprised if each of these has a Step 1 that's something like "Lose to Chokepoint in Ft. Adamant with the Adamant Sentinels on the team (or, perhaps, with a team consisting of the regular Void Guard heroes). Then..."
Malpractice Dr. Medico - Regular VG Dr. Medico deals damage that defeats Skinwalker Gloomweaver on his "Rotting God" side, possibly in Challenge or Ultimate mode.
Road Warrior Mainstay - "After" the events of OblivAeon, says the KS update that introduced these variants, which suggests to me that at least one requirement is to defeat OblivAeon with regular VG Mainstay participating.
Super-Sentai Idealist - ???
Cosmic Inventor Writhe - ???
OblivAeon Heroes:
Akash'Thriya, Spirit of the Void - Have regular Akash'Thriya incapacitated by OblivAeon with the Nexus of the Void as an environment. Then, ???
La Comodora: Curse of the Black Spot - Win a game in the Nexus of the Void with La Comodora active, but at less than 10 HP.
DW Harpy - Defeat Progeny in Rook City with Tachyon (any specific version?) and regular The Harpy on the team. Tachyon must be incapacitated; The Harpy must not be incapacitated, but must not deal damage that reduces Progeny to 0 or fewer HP.
Blood Mage Lifeline - Defeat Deadline in the Enclave of the Endlings. Then, ???
Ivana Ramonat, Luminary - Fight Iron Legacy in Mordengrad with regular Luminary and either America's Finest or America's Newest Legacy on the team.
Completionist Guise - Unlock every other variant in the game. If playing on a platform that supports achievements (I know Steam does, not sure about Android or iOS), may also require completing all of those, though that might be harder to check.
I'm willing to elaborate on where I got these ideas if asked.