I imagine adding new clans would take way less effort than a whole new race. Adding new clans to pre-existing races would mean all the framework, such as models, animations, emotes, gear fitting, etc, are already there. With the most laborious, expensive, and time consuming stuff already done, they would simply have to add new textures, skin colors, maybe a few head and accessory models.

Adding male Viera and female Hrothgar on the other hand would require all the laborious stuff to be done, and would be like adding a whole new race in terms of effort.

https://forum.square-enix.com/ffxiv/...805-09-2019%29