I likewise would be pretty useless in helping to implement this as I'm no mesh-maker by any right, and still pretty new to the modding scene as it goes, but I think that conceptually this is a very good idea. Not necessarily limiting to nude bodies, but I think that there's a lot of immersion to be had by varying heights and body-types of different characters.
As it stands, everybody in Fallout 3, as was the case with Oblivion, is either a ripped, muscular man or a very perky woman (With the exception of children, who are both pretty androgynous). These can be altered with things like BABE, Naouak's body replacers and what-have-you, but regardless every single body is applied to every character. It would be a huge undertaking, but I think that the world would look a whole lot more interesting if there were skinny, pudgy, athletic, average and other type characters populating the world, similar to the
UF3 Female Bodies mod.
To take it even further, linking these to stats like strength and agility would make it even more interesting, though I understand that's taking things too far.
As was mentioned before, I'm sure this would cause ridiculous amounts of damage insofar as killing the GetIsRace calls in various scripts, but as a general immersion mod, I think it would be superb - Like the cosmetic changes in MMM and so on. I've noticed an undertaking that has a similar but still limited effect in SickleYield's
UF3 Default Armor Pack which changes body type depending on the outfit.
If someone's up to the task of also editing the male bodymeshes/textures, I think FO3 could look even better with more varied body types in NPCs and PCs alike.