Essentially, my proposal for a game is to completely change the Player Character's typical role as some vault-dwelling chosen one cast from eden into a cold and uncaring wasteland, into something a little more rugged and a little less glossy. A Super Mutant.
A faction of mutants is on the rise, embittered by constant persecution and convinced of their own superiority, led by a great master/prophet with a powerful secret weapon; a supply of FEV. Now where he got this FEV is open to speculation. Maybe there was a secret storage facility somewhere that survived the destruction if Mariposa? Maybe another secret lab/vault similar to Vault 87? If so, this third vault might produce a completely different strain of mutant, just as the Mariposa mutants were vastly different from the V87 mutants. Perhaps, working with ghoul scientists, the mutants were able to actually reverse-engineer FEV from their own DNA! Whatever the reason, The Prophet is building a new army to conquer the wasteland once and for all, and show those damn bleeders that mutants are the master race!
Or something like that...
Meanwhile, you are either a poor hapless vault dweller, or a wasteland wanderer, captured by a Super Mutant war party and dragged back to base to be dipped! Or injected or however this group decides to do things. They may not have enough FEV to fill a vat, and might have to resort to direct injection, vapor inhalation, or other ways of maximizing the potency of what little FEV they have. The Prophet's eventual goal is simple: Transform all human life on the planet into META-HUMANS, a superior race ideally suited to surviving in the wasteland and rebuilding a new civilization! To that end, The Prophet and his army have conscripted the aid of the brightest scientists they could find, most likely enslaved humans and ghouls, and his supplicants are working tirelessly to breed the army of mutants needed to realize their vision of a united earth.
And as one of their newly minted mutant warriors, it's your job to help them! Or to escape and try to stop them! Fortunately for you, you are one of the fortunate few whose mind survived the FEV Infusion process 'mostly' intact, or at least you didn't end up a mindless half-wit killing machine like most of your new brothers and sisters. Better still, The Prophet has stopped putting those ugly and uncomfortable lip braces in everyone's mouths!
The environment and play style in this game would differ significantly from previous Fallout formulas because, lets face it, Super Mutants are not very popular. Most factions, including NCR, BOS, and Enclave (what's left of them) would happily shoot you on sight, and those who are willing to suspend judgment are generally only 'tolerant' of your kind at best. The majority of your interaction will be with other mutants who have their own communities and sanctuaries throughout the wasteland, including mutants who disagree with or even outright oppose The Prophet! Some human or mixed-race communities will tolerate you and your kind so long as you've got caps to spend, and dont make trouble. You may find some measure of acceptance in New Vegas, for example, like Mean Sonofa[censored] in Westside.
Sadly, as a mutant you'll likely only be able to use custom-modified power armor, if any at all, but thankfully with your thick skin and even thicker muscle, you hardly need the stuff, and you can use any weapon in the wasteland twice as well as any damn Bleeder! The Prophet has his best scientists and engineers working on weapons and armor systems designed specifically for the modern Super Mutant army, re-purposing pre-war technologies into all new Mutant-Friendly arms and armor to help ensure your victory! Just watch out, some of those scientists are still a bit disgruntled at being kidnapped and forced to build weapons for an army of mutant monsters, so they may have sabotaged your gear, just a little bit. Dont worry, though, you're a mutant; lost limbs and extremities will grow back (hopefully).
Basically, I want to see a game where I can play as something OTHER than a human for once, where I'm not necessarily the hero, where it's perfectly fine and dandy for me to be the villain instead! The last two fallout games have tried valiantly toward that goal, with New Vegas coming closest by allowing you to side with any of three morally ambiguous sides, of whom the NCR are arguably the 'least evil'. This game, however, would allow us to actually play AS THE MONSTERS for once, and the ultimate monsters, at that! The Enclave are pretty awful, and the Brotherhood can be pretty bad too, if they decide you have something they want, but when it comes down to it, the Super Mutants are the ultimate evil in the wasteland, and now you're one of them!
So what are you going to do about it, huh? Are you going to run away and join the rebels like an ugly nine foot tall Luke Skywalker? Or will you embrace the dark side, and help The Prophet conquer the wasteland for Mutant Kind, and usher in a new age of peace and prosperity? Or will you just let the whole world go to hell while you explore abandoned subway tunnels and pre-war military bunkers hunting for sweet salvage to plunder? Mutants can be Scavengers too, right?
Personally, if it were up to me, and I had the means and the wherewithal, THIS is the game I would make. We've played Six Fallout games as a human hero. I think it's time for a change. Now lets pull on our Size 32 Boots, grab our Rebar Clubs, and stomp some Bleeders' faces off! KILL THA HUMANS!!! WAAAAAAAAGH!