I dunno...this is one of those details I'm inclined to be critical of. Trek is supposed to be about a brighter future and a unified humanity, where people really are created equal. Yeah, the go-go boots and miniskirts were campy fun, and it just wouldn't be the 23rd century without them, but the complete absence of rank identification is, well, not equal. Or, maybe we'll see some long-sleeve variations, more like the original uniforms. After all, McCoy did have a short sleeve uniform that was bare of rank stripes too..
I wasn't aware that twelve Klingons constituted a swarm...