For non allied races, you require a toon of that race at level 120 exalted with the race's faction. You can use a boost or a race change, it doesnt matter, as long as you do it with a level 120 character with that race and exalted with that race.
Right now only Blood elf and Dwarf heritages are available. Next will be Tauren and Gnomes in 8.2.