If a Fallout game was designed in conjunction with such a feature then the option would be fluid vs 'tacked on' as we see with many of Bethesda's various 'features' today.Д«alancing would actually be very simple, for Super mutants there could be a higher threshold for strength applicable to them, and a lower threshold for other attributes cut off from their special. Realistically the engine(s) could easily support such a function, however games such as Fallout New Vegas, Fallout 3, and Fallout 4 would have to be radically redesigned to support it. Obsidian really wanted to develop in the option to play as something other than human in Fallout New Vegas, but due to time constraints, and Bethesda informing them to explore another direction stopped the effort cold. (Bethesda has no intention what so ever of introducing this feature, and are completely against it.) Ghouls are generally not much of a problem, but super mutants in Fallout 3 and 4 are shoot-on-sight.ДЇrom my understanding the only reason players lack the option to play as various other 'race/species' is due to two reasons, 1 the engine simply could not handle it given the time of development of the project, and 2 due to Bethesda politely informing Obsidian 'that would not be a good idea'. New Vegas also shows the most peaceful coexistence between humans and mutants. Only the Courier is enough of a blank slate to make it feasible for him or her to be a ghoul or a super mutant. The Lone Wanderer is again a vault dweller, so human. The Chosen One could potentially be a ghoul, but not likely. The Vault Dweller is, well, a vault dweller, and thus can't be anything but pure human. I guess New Vegas would be the only game besides Tactics where it would at all be possible to play as ghoul or super mutant. It'd be great to have the option, but it's not going to happen outside PnP versions of Fallout.

And giving the player the option to write their own backstory like in Daggerfall or Wasteland 2? Not gonna happen in a Bethesda-made game.

The story background will have to allow it can't have a fresh vault dweller again if you can play as ghoul or super mutant. I think playing as ghoul or super mutant could potentially work, but all the implications for the story and NPC interaction and general gameplay would sum up to quite a lot.

Fallout 4 play as ghoul