After running into the first BoS knight in fallout 4 all I can think about is a Bethesda made Warhammer 40k RPG. Ok well to be honest an Obsidian Warhammer 40k game.

Think of it a warzone with a few Imperial Guard bunkers and maybe a hidden eldar base to find, Genestealers, hunting down Chaos cults. Different classes to play; Space Marine, Imperial Guard (hard mode), assassin, get to choose new sub classes through special quests like dreadnought or a chaplain. The Guard players could get command of a tank, or go commando. Turn to chaos!

/Coffee rant