If Superman and Supergirl can coexist in this game, then so can Deathstroke and Deadshot. Tons of fighting games have multiple firearm characters. Plus Deathstroke uses a sword, a staff and has ninja training.
Now if Red Hood gets confirmed, that's when you can start worrying about Deathstroke not being in. He's a highly requested character and his shtick is pretty much Deathstroke with a dagger.
Red Hood's always dominated in polls and stuff, so I have no doubt he'll be included and with that said, I am a bit worried about Slade. After his shit treatment in Arkham Knight, don't cut him in Inj 2 also.
Scratch my last post/earlier worries about Slade. Looks like he's probably not going anywhere; if the timing of Deadshot and Harley's reveal solidified anything, it's that anyone notable with a recent strong media presence will no doubt be in this game...
I know a lot of people also want Red Hood in the game and with Deadshot already confirmed, the only way I can see all three of these guys getting in is if they give Slade an almost completely new moveset that makes him less gun-centric and more martial arts based with him mainly using his sword and staff. His trait in the first game wasn't very good so they could give him a stance trait for this one. The first stance for his swords and the second for his staff.
Eh, people said kind of the same about the likes of Johnny and Sonya for MKX when Cassie was first revealed (because she shared some of their movesets, which created initial doubt about them returning). I'm sure they'd find a way to make Slade work alongside Deadshot and (presumably) Red Hood, and even if Slade gets cut, he'll no doubt be one of the most wanted to return long run (whether as DLC or for the next game), as he's always been a high profile fanfavorite.
I agree with your ideas on his moveset though. Always felt he could've been more sword focused in the first Inj, rather than having it for only like two moves. And just to comment on the posted leaked footage for the Batfleck movie, I like the costume design, but hope it still gets touched up on some more, as it still looks like a step down from Deathstroke in Arrow S2.
I voted Johnny Cage on the MK poll, knowing Subby would most likely win. lol Oh well, at least Cage or Raiden will have a better chance for a game like this once Sub-Zero's had his time.
Spawn though, I voted him. I was like wtf when I saw others like Buffy the vampire slayer as the other poll options.