The Fallout universe
I'd like to see the BattleTech universe as well, but it's drawcard for me was the rich and byzantine politics that surrounded the Houses of the Successor States - any movie would be a MechWarrior knock off, with Johnny Everyman fighting off hordes of mechs in his damaged mech...that being said, the last stand of Aidan Pryde at Tukayyid would be worth it
a Warhammer 40K movie would be cool, but there's so much background fro that universe that it'd be impossible to condense it into a few hours...
On a personnel note, I'd like to see a movie about the Battle of Ulus-Kert - probably too soon, but those Russian soldiers deserve more recognition than than they got.