I thought about this, but my line of thought went like this: People like the modularity in dwarf mode, because they are used to vanilla DF, and they dont like specific themes like muskets or magic added to them.
But with the new races, its all exclusive content, no one knows how Gnomes or Succubi or Orcs or Warlocks are played in vanilla, because they dont exist. Taking away single parts doesnt make them closer to an idea that the player is used to from playing vanilla df.
this is the first request I got about it. Its certainly easy to do, but would in the end add 6 new tabs to the GUI, one for each race.
Swapping buildings between races is not possible without heavy modding though, at least when they use special syndromes and scripts that are fitted to a specific race. The skeleton inscriptor would never work on other races, or the dwarven prison would transform an Orc you play into a "imprisoned dwarf". So thats not really an option.