there are a few ways how they can fit naga in looks wise.
a: look at druids. cat and tank druids do not have the option to see theyr gear in combat. aslong as the upper half would be visable it already would beat those.
b; restrict naga to caster classes. priests mages warlocks shamans all use dresses pretty much exclusive. for the odd piece that is not a dress they could easy make a retexture like they have done before. (many pieces these days have a pants and a dress version) or the lower half could simply be inviseble if its not a kilt / dress.
c:sudden cure has been found to cure the naga curse! /waggles hands magickle) you now can transform like a worgen from high elf to naga form. there profit