An upcoming event listing at Gen Con may have leaked some upcoming plans for Marvel Champions: The Card Game. Fantasy Flight Games has listed several events for "Marvel Champions: Mutant Genesis" on the official Gen Con events page. The events are for a Marvel Champions play session, so the assumption is that the events will be for an upcoming Marvel Champions expansion product, likely a campaign box that will kick off a cycle of new card releases. No other details were listed about the events.
Marvel Champions: The Card Game is a "living card game" published by Fantasy Flight Games. Unlike collectible card games, players are provided with specific collections of cards with every purchase, so there are no card rarities to follow. In Marvel Champions: The Card Game, players build a Hero deck built around a specific hero and one of four aspects (each of which emphasize a different play style. Players then use that deck to complete scenarios involving one or more supervillains. Marvel Champions can be played as either a solo or co-op game, with individual scenarios and a campaign mode available.
While Marvel Champions is about to enter its fourth year (the card game was a Fall 2019 release), the X-Men have not made a formal appearance in the game outside the occasional piece of card art. If "Mutant Genesis" is indeed a full campaign box, it will likely include two X-Men heroes with subsequent months adding additional X-Men through Hero Deck releases.
Currently, Marvel Champions is in the middle of a Spider-Verse focused cycle of heroes. Upcoming releases include Spider-Ham and Sp//dr, both of which followed the release of the "Sinister Motives" expansion that added most of Spider-Man's iconic villains to the game. Both Spider-Man (Peter Parker) and Green Goblin were already included in the game through either the Core Game or via an Encounter Pack expansion.
Expect to hear more news about the next Marvel Champions cycle soon.