Any modifications needed for Elezen are also needed for Lalafell and Au Ra.
(And occasionally they forget to do that. There's one hairstyle - it looks like a shorter version of Urianger's hair and is next to it in the list - that doesn't have an 'opening' for ears and they just clip straight through.)
As I said earlier though, I really think that whatever is causing this lack of availability, it's not just a matter of the time it takes to adapt it.
I'm not saying the lack of hairstyles is necessarily justifiable, just that it seems like the reason must be something more than "they were lazy and decided not to do it to save work", because it doesn't seem like it would be that much work in the grand scheme of everything they need to do.
They avoid explaining their technical issues, but I think there must be one. Somewhere. Surely they have more pride in their work than to leave it undone because they could do it but don't want to.
Hairstyles might come eventually, but they said early on that headgear wouldn't display at all - it was a design choice, not a scheduling issue. The things that did get added due to player request are ones that don't interfere with the hairstyle but sit over it or on the face.
I don't know about Viera, but I'm assuming that Hrothgar wouldn't be able to partly 'switch off' the hair model when hats are equipped, because of how they've been implemented as part of the face and not the usual hairstyle setting that's instead controlling their fur pattern.
Actually, Miqo'te ears are modelled into the hairstyle itself. It's a different system to Viera ears that are a separate element of the model.
You do realise that's the one independently-released Korean set that hasn't been approved to be put in the main game? Everything else (to my knowledge) has been transferred over, including things implemented later, and despite requests for it to be added.
The other complaints about hairstyle clipping are valid, but that screenshot is what people post to demonstrate why that dress isn't available.