Hmm
to be truly unique and outstanding or special, one race mustn't be available easily.
If everyone is unique, no one really is.
The vampire spawn is one case.
Maybe some sort of achivement, beating the game in a difficult setting or very different setting will unluck a truly unique race that was never ment to be there in the first place but makes a rerun very intresting?
A lawfull/good run unlocks your Aasimar or a Dwarf (male) and Elf (female) 2 person only party unlocks a strange dwarf and elf halfblood mix that has grace of the elf and boldness of a dwarf. Sounds like a sushi wrapped in bacon..