Ok, so I got my copy of Shattered Timelines yesterday, and looking through it I found a couple hints regarding future heroes. I'd like to preface this by clarifying that all of this info comes from my hard copy of the game, and is NOT PLAYTESTER KNOWLEDGE.
First is on the Dreamer's card, Projected Paralysis. In the background is a gigantic red lady apparently being attacked by the Dreamer. Because of this, it is fair to assume she is a hero. However, one thing no one else has mentioned is her uncanny resemblence to another character. She is huge, has red skin, and bony spikes protruding from her shoulders and elbows. She is, undoubtably, a female Thorathian.
Second comes from Miss Information's "Insider Knowledge." She is shown using a computer to research the heroes' weaknesses. Each hero has a designated folder, and they are arranged alphabetically. However, there are 20 folders... and only 18 heroes. The strategically-placed glare covers up any spoilers, but you can still arrange the heroes in order to determine where the missing spots are. (There's one between Haka and Legacy, and another between Omnitron-X and Ra). The first one has -yfe in its name, and the second appears to begin with either Par- or Pan-. Given that there are only 2, I would guess that this does not include the Vengeance heroes for whatever reason. Maybe they're Red Herrings, but maybe they're from the next expansion!
Given that Unity and The Scholar are both promo heroes, maybe they really don't have folders here. Alphabetically, they'd both have to go in the spot which I'm guessing is Tempest.
If so, that leaves four unidentified heroes.
It may be that _NONE_ of the heroes from Vengeance are represented, for whatever reason, and the other four heroes represent decks that we will see in the planned fifth and sixth expansions for Sentinels.
Also in the Dreamer's deck on the Whipacorn there is flavor text from a character named Mainstay. Since it isn't listed in Miss Information's Insider Knowledge card and if that card does list heroes after Vengeance, then Mainstay may be in Vengeance?
It's possible that Mainstay is La Capitan's nemesis, and is also the guy Legacy is punching in Iron-Fist Strike. They do have the chains in common, at least.
I have a strong feeling that La Capitan's nemesis won't just be one hero--I think there will be four characters, but all in the same deck. Look at her hero's icon: there's four distinct things that are totally different from one another. Also, Christopher once made a comment implying that though there are 5 hero decks and 5 villain decks in Vengeance, that didn't mean there would be 10 characters in Vengeance. And since it doesn't make sense to be below the number of decks, that would mean that one deck would have to contain more than one person (excluding Proletariat's clones).
Plus, on her flipped side, La Capitan is divided into four sections. I think the idea of her being in four places at once is another indicator that she's angered four people.
In Unity's case, could it be because she is an intern that she hasn't graudated to "Full Hero" and that she isn't viewed as a "threat." It would seem there is some information that either hasn't been plugged in yet, so there wouldn't be a folder?
Also can anyone post a screenshot of the picture(s) in question. I haven't gotten my copy yet (I'm sitting at letter T...so yes it's gonna be a while) and its driving me a little nuts that I can't not only see what's going on, but I can't try to run it through photoshop (not that I may or may not succeed)
Looks like these are listed in alphabetical order, which would mean the one ending with "yfe" would have to start with H, I, J, K, or L. The one ending in "ck" would start with R or S, with a slim chance of starting with a T as Tachyon is Ta-.