To start off with, yes I stole Foote's use of his name in naming his lore discussion thread. I liked it and I have just enough ego to copy it. I am not saying I will set up as a good a thread; I most likely won't because I will not have any contextual evidence or links. I have neither the time nor my cards to provide this, but I will try my best to otherwise back up my assertions.
So with that out of the way, let's get to the subject at hand. Villains who may become someone else, something else. These are guesses; I don't have any definitive proof or any real confidence in these with exception of one. So to start off I'd like to give reasons why I think we will be getting hero decks for villains, then get started on specifics.
The final mega expansion that everyone on the forum has been speculating on is likely a fight against this big being that comes to Earth to eat it. That's the most prevalent theory and the one I'm going to use as my premise. This will be a multiverse ending event, it's going to be scary and even the bad guys are going to want to do something about it. The last expansion is going to be a mega expansion; Vengeance had five heroes and a new game mode, meaning this one probably will as well. So we need 5 new heroes, and we are out of hints. We have had a picture of Capt. Cosmic since IR came out and a pic of Sky Scraper since ST. We don't have more pictures, so these heroes probably already exist somewhere, and the most likely place is as villains. I may go into more detail later, but for now this is my premise and I want to finish my list before I get bored typing this or forget what I was going to say.
My list (in no particular order after the first couple) is as follows:
1. The Matriarch- So with the second core Tactics game we see she eventually becomes a hero. We theorized this would happen, from Reveal the Flaws, the fact she was mostly a missguided teen who was way too into Poe, and the fact Christopher said she's important for the end of the story. Other people have explained her place on this list way better than I can/ will so I'll let them if they want to.
2. Blade- So this one seems a little out there, but stick with me. We have been told that SotM is a complete story. The beginning of the story was Legacy and Blade. The end to some extent has to have some interaction there. Vengeance could be looked at as that interaction but I would argue otherwise. Blade beat Legacy, but not permanently and with little (as far as we know) ultimate change in the relationship. We need that final conclusion and I think them temporarily working together does that. We also need to know how Blade gets youthened for Tactics.
Another idea I had along this line is that instead of it being the Baron, it's his daughter. I like the symmetry ( I could not for the life of me figure out how to spell this, I ended up having to google it) of the legacy of the rivalry continuing beyond the present. This fictional Baronness Blade would be not enamored of Legacy and the Freedom Five in general, but wants to redeem her family's name. She would likely have similar motivations as the Baron does, but puts her motivation into helping people
3. Akash' Bhuta- I know, I know. She isn't exactly sentient, or really quite a bad guy. That's why she is on this list. She would oppose the destruction of herself aka the Earth. This being of Order / Chaos ( I've seen strong arguements for both in the last couple days) is coming to destroy her, and she would need to destroy it or be destroyed. Her power could be equivalent to other heroes pretty easily: she has been thoroughly thrashed by the Prime Wardens at this point and hasn't recovered yet.
4. Deadline- His whole goal is to prevent the Cosmonautilus (the big bad from the last expansion, I just love that name) from destroying Earth. He fails through his own methods, so he teams up with those he previously lost to to stop it. Pretty simple and if you want more explanation I'll elaborate later.
5. Dawn- At this point I'm actually pretty sure these villains won't appear but I can get I decent explanation for them doing so. Dawn is a leader of people. She has some feeling of responsibility towards them. She will stop those who will try to destroy her citizens.
6. Apostate- He is cast out. He is, if Foote's threads are to be believed, someone who is about to be in a lot of trouble if the Cosmonautilus finds out he is alive. He sees the only way to survive as teaming up with the heroes.
7. Infinitor- He was once a good guy. If he regained his sanity, he likely would be again. He also might want to make up for his past mistakes. I don't like this one because he would be extremely similar to both Capt. Cosmic and Omnitron X, and I don't think the GtG people will do that. But I included it because it had a decent justification and I like the story implications if nothing else.
So that's what I came up with. I know most of these don't have great justification and a lot of it is subjecture and daydreaming. I also know we have no proof that the final expansion has heroes to begin with. And I haven't looked through the cards for Wrath yet, so I could be wrong about not seeing any more heroes.
I hope you enjoyed my Humble thoughts, and let me know what you think.
Phew, that was a lot of typing...