The crown store being quite full of cosmetics I think character sound packs that were more distinct/unique could be extremely popular.
The current selection of grunts, moans, bellows, and snorts in the character selection are not very distinct and do not really cover different character types/styles. I have a fairly young caster character and the character sounds just do not match the character at all. Most of the female character sounds are very tuned towards melee brutish Briene Tarth types of characters. There are no higher pitched voices, none that have a more whispy sound, none with a mischevious tittering laugh, ect...
ZOS could build packs with character types in mind, much as they do with the personalities.
A assassin type sinister sounding character that has combat sounds where they seem to sound like they are taking pleasure in the attacks, a creepy laugh, and almost an almost disgusted sound of indignation when getting hit.
A regal pompous Abnur Thorn type of caster sound pack.
An evil caster archetype for necromancers or vampires that catches into something similar to the Vincent Price vibe (the voice in the Thriller video).
For female characters there are a lot of options as well. Higher voiced characters that might have a voice more like Harley Quinn in the animated stuff.
Getting voice actors to create these packs should not be terribly expensive, the number of sounds is quite limited and most voice actors could knock out the recordings fairly fast.
I think a lot of people would be interested in checking out the packs and if they are done well many would buy the ones that fit their character well and create a more complete character not only in looks and personality movements, but now their voice/sounds as well.