There have been a number of previous attempts made at getting the ball rolling on a Fallout movie, including one promising project that was ultimately cancelled. The fact that Bethesda holds a ‘Statement of use’ Fallout movie trademark covering “motion picture films about a post-nuclear apocalyptic world” does give hope that we may one day hear the words “War. War never changes” on the big screen.
A movie incarnation could use Fallout canon taken from the entire series of games. Post-apocalyptic movies are nearly always popular, and with Mad Max becoming a lot of people's ‘movie of the year,’ as well as Fallout 4’s recent release, Hollywood would do well to ride the momentum and get a Fallout movie into theaters asap.
For inspiration, 'Fallout the movie' should look toward Denzel Washington’s awesome The Book of Eli, which shows exactly how to create a post-nuclear world. Of course, it would need to add in the game's famed advanced technology (power armor!), and having some deathclaws and mini-nuke launchers wouldn’t go amiss either.
Protagonist: Pretty much anyone, really. Well, I don’t think Jim Parsons would fit the role, so maybe not anyone.
Do not cast this man!
Antagonist: Again, it all depends on what lore the movie uses. Although I always thought Neal McDonough (Arrow’s Damien Darhk) would make a great Caesar from New Vegas.