Well, you could rule out dresses altogether (not that I care for them). You would see the "human" upper half dressed up, while bits and pieces of the armor or "street clothes" adorning the horse half. They could even give females the chance to have their tales braided/preened while wearing some of the more fancy stuff.
Plus they already have some sexy armor that fits the horse half-
I guess I hate to see such a good race with many potentials just discarded by most MMORPGs/RPGs/Table-tops. And I know that ArenaNet would implement them the right way, and not disappoint.
Plus, it would be another unique race to add to their repertoire that they already have going.
Know what, I'm going to make a huge email about these guys and send it to them. Suggestions are a plus!