The ranking currently looks like this:
Basically lock-ins: Giorno/Joker, Catwoman/Black Cat, Thor/Vegeta, Ant-Man/Atom, Jason/Micheal, Lui Kang/Jago
Probable: Shulk/Lightning, Cole/Alex, Dante/Kratos, Palpatine/Xehanort, Bowser/Eggman, Scarecrow/Mysterio, Simon/Kyle, Meta Knight/Zero, John/Raidou, Scarlet Witch/Zatanna, Fire Emblem, Hunter X Hunter
50/50: Spawn/Ghost Rider, Vader/Obito, Vader/Saber, Mac/Ippo, Captain America/Kamen Rider Ichigo, Eggman/Wily 2, Ash/Yugi, Cell/Dark Samus, Mewtwo/BlackWarGreymon, Gogeta/Omegamon, Aigis/Noel, Master Chief/Doomguy 2, Doomsday/682, Bradley/Solidus, Destoroyah/Iris, Omni-Man/Bardock, Taskmaster/Deathstroke, Cervantes/Spinal, Steve/Terrarian, Raz/Ness, Escanor/Whitebeard, Guilty Gear in general, Asura in general, Magneto in general, Ridley in general, Yusuke Urameshi in general, Spiderman in general
Don't count on it: Dante/Deadpool, Yu/Josuke, Chie/Mako, K. Rool/Blackbeard, Spawn/Demi-Fiend, Hit/Sakuya, Omni-Man/Homelander, Ragyo/Lusamine, Bill/Discord, Saitama, Sinestro, Guts
lol no: Goku/Superman 3, any MLP matchup other than Bill/Discord
Which matchups/characters have I overlooked?