So the way I envision it, MVC4 (I'm just calling it that from now on) would go back to 3's comic book artsyle. But I say go even crazier. Make everything look even more like a comic book, go NUTS on the lighting engine, all that jazz. Also, have an in-game store with in-game currency (NO MICROTRANSACTIONS), where you can buy all kinds of cool stuff. Costumes, extra intros and victory screens, alternate music tracks, artwork, make the unlockables actually worth it unlike most Capcom fighting games these days. Also, bring back arcade endings, but also have arcade BEGINNINGS, and have some of the arcade modes throw in some extra fanservice. For example, Mega Man's Arcade Mode begins with the robot master select select screen, and you can select any of the fights in whatever order you want instead of fighting in a set order like the rest of the arcade modes. In terms of gameplay, you have the option to do either 1v1, 2v2 or 3v3. So you can fight like a traditional fighting game, fight in Infinite's gameplay style since that's like the one thing Infinite did right, or you can simply engage in some pure good old-fashioned Mahvel. X-Factor is completely gone and the Infinity Stones are a separate mode. One last thing: make it a celebration. Make it a celebration of Marvel, make it a celebration of Capcom, and most of all, make it a celebration of Marvel vs Capcom itself. Have tons of nods to earlier games, what if we had footage from previous games in the background of the character select screen, what if we had completely remade versions of classic stages as unlockables, all that stuff, pull a Smash Ultimate and show off MvC's history as much as possible.
Aight, roster time: newcomers are in bold and characters who haven't been seen since 2 are in italics.
Capcom:
Ryu
Chun-Li
Morrigan
Zero
Strider Hiryu
Tron Bonne
Wesker
Phoenix Wright
Dante
Vergil
Monster Hunter
Mega Man
Captain Commando
Juri
Mike Haggar
Akira Kazama
Jon Talbain
Lady
Jill Valentine
Franziska von Karma
Hayato
A Cyberbots rep (either Jin or Devilotte)
Viewtiful Joe
Amaterasu
Frank West
Edward Falcon
Nina
Asura
Marvel:
Spider-Man
Iron Man
Captain America
The Hulk
Thor
Wolverine
Storm
Magneto
Deadpool
Doctor Doom
Captain Marvel
Black Panther
Thanos
Scarlet Witch
Star-Lord
Psylocke
Daredevil
Venom
Kamala Khan
Doctor Strange
Blade
Gambit
Fantastic Four (with Mister Fantastic as the main fighter and the others popping up for most attacks)
Black Widow
Squirrel Girl
Gwenpool
Green Goblin
Shuma-Gorath