Spider-Man's roster selection will especially suck. In the MCU? He'll only have Vulture and Shocker to pull from. Unless there's some other of his villains present in Homecoming we don't know about yet.
This also cuts out new Marvel favorites from the books like Kamala Khan, Miles Morales, etc.
Would you be able to do people who haven't debuted yet but are planned? Like Carol Danvers? Do you include her?
It likely wouldn't rely
strictly on the MCU. For example, Spider-Man would probably stay as an adult, since all of Peter Parker's Capcom fighting game appearences are based on 80's/90's Spider-Man. You can tell from the ways his eyes are drawn on his mask, very Mark Bagley-ish. And how he has fairly normal but muscular arms, but big thighs and feet. Hawkeye has first seen in 60's costume for example in MvC3, and that game also had been influenced by the movies(see Hawkeye and Rocket Raccoon, if I'm not mistaken.)
They would likely take the major players from the movies. Some supporting cast from the new cartoons/comics such as Ultimate Spider-Man. The show isn't great, but it has a ton of villains and supporting heroes to pull from. I'd rather have Classic Venom or Agent Venom, since he'd offer more than Miles, who'd end up being the Ken to Spider-Man's Ryu. And Marvel will keep whoring out Spider-Gwen for some reason, instead of Silk, who's kind of cool.
Even if they reigned it in for the MCU, this still can include the Netflix shows. Daredevil, Punisher(who is technically a Spider-Man character, given his debut in the comics.), Elektra, Luke Cage and Iron Fist are also going to be pretty relevant to the current Marvel era. Kingpin too, but he doesn't have any major weapons to set him apart from the rest, maybe his pimp cane.
Carol Danvers was ruined in Civil War II, so she can screw off for now.
Really, the only major loss here is the X-Men, Doom and Super Skrull.