3) Move The Action Into Outer Space
Common sense says that whatever the next Fantastic Four movie does to try and recapture the attention of moviegoers will need to drastically shake up the franchise. More of the same simply won’t work; the dark and moody tone of the reboot didn’t connect with anyone, and the “grounded” approach which worked so well for Christopher Nolan’s Batman movies felt as out of place here as it did in The Amazing Spider-Man back in 2012.
So, while some tonal changes are necessary, so too is perhaps the general setting of what comes next. Why not send the team into space?
Some of their greatest adventures have taken place off planet. Blasting through alternate realities and the far reaches of space could turn the franchise into a full on sci-fi series, and that would actually be a move which would feel fresh and exciting; it certainly worked for Marvel with Guardians of the Galaxy after all.
With a team of four humans granted very unique abilities, it would be fascinating to see how they interact with aliens (and vice versa), and if it leads to an epic battle with the aforementioned Skrull Empire, then the next Fantastic Four movie could really be something special.