What if the reason why there isn't a new race is because...

[Theodric]

2.0:
-Sudden influx a Miqo'te men
-Sudden influx of Highlander women
-Sudden influx of Roegadyn wom-...oh nvm that

3.0:
-Sudden infestation of Au Ra, a race never known to exist.

The developers simply realised what a terrible concept gender locked races were. Furthermore all of the original races were already well established within the setting. Au Ra weren't but at least they came from Othard - somewhere we haven't seen in-game yet. With that said, though, they ended up being less 'bestial' and more like the other existing races. Which led to many people finding them to be rather lacklustre.

That doesn't really change the simple fact that half-elves have already been established as rare and heavily shunned. Elezen exist, Hyur exist - just expand the options available for both races instead of wasting development time on what will essentially just be a Midlander model with Elezen ears stuck onto it.

Thankfully this setting takes itself seriously enough that dumb combinations like Roegadyn/Lalafell hybrids won't likely ever be a thing either.

Maybe in 5.0 we'll get a new race. Who knows? It's not a priority when the existing races are in dire need of additional customisation options and representation.