Not a mod, but MCU doesn't include X-Men etc. because those franchises are owned by other production companies (Fox has X-Men, Columbia has Spider-Man). Scarlet Witch/Quicksilver in Avengers 2 legally can't, as far as I understand it, reference X-Men or mutants or anything (so how they'll get around that is...uh, we'll see, I guess). Those other films you mentioned might be Marvel characters, but they don't exist in the same shared universe--the Fantastic Four do not exist in Tony Stark's New York City, and so on, at least not until rights revert at some point, at which I expect they'll milk that cash cow, haha.
MCU films are Iron Man 1-3, Incredible Hulk (2008, not Ang Lee's Hulk), Thor 1-2, Captain America 1-2, Avengers 1-2, the upcoming Guardians of the Galaxy and Ant-Man. Marvel One-Shots and Agents of SHIELD also qualify (sidenote though that Joss Whedon isn't the showrunner for AoS; he directed and helped write the pilot episode, but the actual showrunners are Jed Whedon and Maurissa Tancharoen). I think you can debate the canonicity of AoS since it's a TV show involving side characters, but it's clearly meant to be part of the same fictional universe.