This is likely trolling and I have a reason to believe it that way. I went and read over the official interview with Boon from GI and then read into more sources that also decided to talk about the same interview and looked over many of the statements being made and here are my findings.
A guy at GameFaqs is claiming to know as well, but has no credability at all and his claim is:
1. Lobo: first week of june- supposed to play like kratos only faster
2. Martian Man Hunter: late July early August - all I was told is he's a complex Zoner.
3. Atrocitus: September - most damage out put in the game, plasma blazer that does more damage the further away the opponent is.
4. Power girl: October- he said like Superman without zoning tools.
This has no merit as he is also claiming other characters(around 5 or 6 more) will be coming later in the year after August time frame, the Season Pass states August time frame for the last piece of DLC, but that doesn't mean no 2nd season is possible, but it is easily assessed that those plans are not even currently on the table either.
For the above claim about the INI file, there is two dead give aways that it is likely false:
[UnlockedDLC.Characters]
+Unlocked=CHAR_Lobo
+Unlocked=CHAR_Batgirl
+Unlocked=CHAR_Scorpion
+Unlocked=CHAR_Zod
+Unlocked=CHAR_Aquaman_A
+Unlocked=CHAR_Bane_A
+Unlocked=CHAR_Batman_A
+Unlocked=CHAR_Batman_C
+Unlocked=CHAR_Batman_D
+Unlocked=CHAR_Batman_E
+Unlocked=CHAR_Catwoman_A
+Unlocked=CHAR_Deathstroke_A
+Unlocked=CHAR_Flash_A
+Unlocked=CHAR_Flash_B
+Unlocked=CHAR_GreenArrow_A
+Unlocked=CHAR_GreenLantern_A
+Unlocked=CHAR_GreenLantern_C
+Unlocked=CHAR_HarleyQuinn_A
+Unlocked=CHAR_Joker_A
+Unlocked=CHAR_LexLuthor_A
+Unlocked=CHAR_Nightwing_A
+Unlocked=CHAR_Shazam_A
+Unlocked=CHAR_SolomonGrundy_A
+Unlocked=CHAR_SolomonGrundy_B
+Unlocked=CHAR_Superman_A
+Unlocked=CHAR_Superman_B
+Unlocked=CHAR_Superman_C
+Unlocked=CHAR_Superman_D
+Unlocked=CHAR_WonderWoman_A
+Unlocked=CHAR_WonderWoman_B
+Unlocked=CHAR_WonderWoman_C
Read the pattern, each character has an alternate, the Insurgency/Regime costume, as one can easily see that it would likely be named so in the actual file, if this is only the files that involve the Season Pass only, then likely you wouldn't see missing varibles, why is that Batman has cotumes listed A,C,D,E, yet almost all the others with more than one costume are listed with A,B,C,D and so on, its too inconsistant especially on a programmer's standpoint.
Finally there is one piece of evidence that trully denounces this claim and should be what will put it to rest already and that is a actual statement made by Ed Boon "
In terms of costumes, there's a lot to pull from, the pre-order bonuses, collector's edition, etc. Is the plan to include costumes with each of the DLC characters?Yes. This game has literally over 100 costumes between pre-order stuff, the ones you can buy, and the ones packed in the game. There's a ton of them. Giving people costumes is the way we can push the other content. For instance, if you download Lobo, we want it so you can play Lobo against me, but I need to have the Lobo content on my machine for you to use him against me. The way we're going to do that is to give away costumes. When you get your free costumes, you'll also get the necessary content to be compatible with everyone, so there's no issue of people not having downloads." Whcih within the statment he very easily hints at the DLC characters and all having adduitional costumes.
There is a huge possibilty I am incorrect on this assessment, but this claim seems too inconsistant.