In the summary, Josh created the arc for Cass, including end states with character state changes depending on how her main quest resolved. I only did minor iterations on it (keeping the fate of her Dad in question and changing some elements), added elements about how she felt about the other companions, but I liked the initial direction very much, so much so it was really quick to write her. Josh left the tone and actual implementation up to us.
We did iterations on her perks to make them more personality-centric (Cass's initial perk was carrying more Water, or giving a bonus healing for Water), but after kicking it around with Josh, we settled on the Whiskey Rose perk which we thought would make her more valuable as a companion game mechanic-wise and also reinforced her hard-drinkin' personality.
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Wild Wasteland was an idea by Josh Sawyer to allow folks who wanted those optional references in the game. I don't think it was directly inspired by Fallout 2, it was more the feeling from reading the forums that there were a certain % of folks that did very much enjoy those aspects of Fallout (including folks who would enjoy hardcore mode, who enjoyed references to Aliens). Josh is considerate to the player experiences, and he leaves aspects of gameplay like that as an optional choice for players without forcing it on them.