They seriously just need to change the little shop on DS9 into an 'Elim Garak House of Couture' and stock it with all the costumes and uniforms we'd ever want. And maybe a long suffering Holo-Garak (with Andrew Robinson's voice, of course) to nitpick about our fashion sense.
That said, I'd like to see more civvie stuff: jewelry/body piercings, long and short dresses, shawls, looser/lighter fitting jackets, tops and pants/skirts, short robes (things that look more comfortable to be in), sandals, open backed tunics.
Hairstyles- just nicer hairstyles for females. And I've posted about this elsewhere, but, more elaborate, high browed updo options for female Cardassian aliens and Klingons.
Body tattoos/paint/henna-esque decorations for the arms/hands/ legs/feet/back/shoulders/belly
This, with Andrew recording various "rumors" regarding upcoming content and events, that holo-Garak can spout off while you are making your uniform changes in the costume interface window. When you finally make your selection, he can finish with, "But what do I know, I'm just a lowly tailor. My my, doesn't that look magnificent on you!"