Last Friday, a rumor started on NeoGAF about the possibility of Marvel vs. Capcom 4, with a planned unveiling at PlayStation Experience 2016. Today, Polygon is reporting that multiple sources have backed up this rumor, stating that the game in development and scheduled for release in 2017.
Polygon also reports that the Marvel side of the game will focus on characters in the Marvel Cinematic Universe. This means you can expect the Avengers - Iron Man, Captain America, Thor, and Hulk - alongside other heroes like Ant-Man, The Guardians of the Galaxy, and Doctor Strange. This also means it's unlikely that classic MvC mainstays like Wolverine, Magneto, and Storm will be making an appearance. Likewise for Doctor Doom, whose cinematic incarnation is also owned by Fox.
The last release in the series was Ultimate Marvel vs. Capcom 3, published on PlayStation 3, Xbox 360 in 2011 and on PlayStation Vita in 2012. Prior to that, Capcom released Marvel vs. Capcom 3 in early 2011. This would be the first game in the series to leave behind the X-Men characters, who've been with the series since the first Marvel-themed Capcom fighter, X-Men: Children of the Atom.
A Capcom spokesperson told Polygon that the publisher "does not comment on rumors or speculation."