It pisses me off to no end, the fact that Nightwolf, Fujin and Sindel were all present in the story mode but weren't actually playable.
Instead we got Jason Voorhees, Leatherface and Alien because everyone wanted those characters.
I feel like Night Wolf needs a character revamp before he comes back - look at what Killer Instinct did recently with their Native American character (consulted Nez Percé to be more thoughtful and culturally sensitive) recently.
Fujin was the one character that really made me scratch my head. I'm guessing they held him back for MK11. Truthfully, I liked Bo Rai Cho's story portrayal, and was excited to see him come out, but when his fart/puke moves were part of his base move set and not just an optional funny loadout, I was let down. I feel like they could have really turned the corner on that character.
Anecdotally, when Alien, Jason, Leatherface and Predator came out, my non MKX friends wanted to come over and see them, so it makes sense to me that the guest characters are so prominently featured in NRS games. That said, this is another vote for "I hope they limit the number of guest characters to 1-2.
I have been really enjoying every DC character in this game, except Joker (that design just feels off to me - stuck between younger, emo look, overly designed gear and a harsher older voice) and to a lesser extent Poison Ivy (but if they release an animated series gear set or something a little less plastic Halloween costume looking, I'm in). Most of the names that are getting thrown around I'm not super familiar with, but would be excited to learn more about.