I think the best way to go about this would be to have a group akin to the fans (though obviously with their own twist) dealing with the events leading up to the end of Hotline Miami 2, or possibly have it be set before the first game.

A new gang or mob could be introduced to give the group a common enemy, and obviously it would deal very heavily in drugs, sex, and the other neccesities of an 80's Miami vice setting.