When designing huge sprawling open world games, curbing feature creep at the start of development is profoundly important. If you start with too broad a scope, a project can quickly become unwieldy, and impossible to polish properly, so often ideas thrown around early in development need to be scrapped. One such early idea was the concept of having multiple playable races in Fallout: New Vegas.
According to an interview conducted by Eurogamer with Obsidian CEO Feargus Urquhart, players would have been able to choose between playing as a human, ghoul or super mutant. Bethesda quietly nudged the developer away from the idea, suggesting that it would be a nightmare to implement due to the ways it would complicate the weapons and armour systems in-game.
It's always interesting hearing about the things that might have been in games. Imagine how this might have changed how people reacted to you in New Vegas. Maybe if we're lucky, we'll see this feature resurface in some future Fallout title. The full Eurogamer interview on Obsidian's recent fortunes is well worth a read.