Imo currently the most customizable WoW race based on in game cosmetics & mounts has to be Pandaren between MOP:Remix & MOP TW 
%. Blizzard has to know this hence why we haven’t any word on a Heritage armor set for them. I’m sure we will still get one but it’s definitely NOT a priority with all of the Pandaren based cosmetics being currently released in game. I have a few Pandaren alts so I’m pretty happy rn