Characters I've leaked for MvCI previously include (I won't put check marks by the ones not yet revealed, but since Ryce leaked them, I'll put an asterisk to be nice):
Spider-Man *
Doctor Octopus
Venom as DLC
Songbird
Ms. Marvel
Ant-Man *
Rocket (but Groot is now part of his moveset) ✓
Thanos *
Black Panther
Doctor Strange *
Star-Lord
Black Widow
Chun-Li ✓
Hunter (from Monster Hunter) *
Rathalos (though I will admit that this one is shaky because they might've nixed it to only be in the Hunter's moveset for a Hyper because Giants might be done away with as playable, and Rathalos was planned to be part of the Hyper regardless) Note: I haven't heard anything since regarding Rathalos
Strider Hiryu ✓
Leon Kennedy
Jedah *
Nathan Spencer *
Captain Commando
Dante *
Frank West *
Asura
I was also told of a Street Fighter V and a 3rd Darkstalkers character, which I'll get more into in a moment.
DLC characters I heard about were Doctor Doom, Super-Skrull, and Silver Surfer. As well as X-Men being DLC. The ones I've heard for the longest time being Wolverine, Cyclops, and Deadpool.
Note: I said that not ALL the Capcom characters I leaked are launch characters before. And I never had confirmation that ALL the Marvel characters would be either, neither did I say they would be. So fuck off with that shit claiming I said things that I never actually said before. People just assumed I did because they're mad that Capcom bunglefucked the launch roster. AND YOU SHOULD BE.
So moving right along, I've recently heard of plans about Season 2 possibly being Fantastic Four vs Darkstalkers DLC pack next year, which is how Doom, Skrull, Silver Surfer, and She-Hulk will be an 8 character season instead of 6, and mentioned Felicia and Talbain by name as Darkstalkers being added for it. Hsien-Ko's return could happen in that too to fill a slot and because they can reuse animation assets from MvC3.
Then the Season 3 plans be that X-Men are seemingly going to be added alongside some Street Fighter characters to play on the X-Men vs Street Fighter part of the MvC legacy. Which makes sense since SF only has 2 of them at launch as reps.
Season 2 and 3 from what I know and hear, won't be released like SFV does with the all year thing to only add 6 characters, but instead one season in the first half of the year, and the second in the second half of the year. Though there is some kind of discussion going on about doing 4 seasons a year, meaning a season every 3 months (like actual seasons of the year, though not accurate probably as they'd follow January-March, April-June, July-September, and October-December).
They went in a direction of making this game VERY DLC-heavy. Which as you've seen, is an extremely controversial decision. It's bad. But they made their bed. And honestly, despite having a source knowing someone who works for them, they as a company piss me off, which is kind of an ulterior motive why I leak stuff. Aside from just being bad at keeping secrets tbfh.
I think the thing that bothers me as a fan so much is how they're witholding so much and so many of the most requested characters as DLC and essentially filled the roster with some characters they knew people wouldn't pay for. But peppered the roster with some enticing things like X, Jedah, and the Hunter on their side to try and coax you to. The Marvel side is its whole other issue that so many people have gone over and over, but both sides are littered with scummy corporate bullshit.