Long-sleeve tunic shows rank.
Short-sleeve minidress - no rank. It would seem any female officer wearing it is known to one and all throughout Starfleet and perhaps the Federation, thus everyone will be able to properly address the officer! None of this "Ensign Uhura" crap.
EVERY UNIFORM NEEDS TO DISPLAY THE RANK OF THE WEARER. How frikkin' hard is that for a costume designer, cripes.
It hasn't been a rule in previous Treks, so why should it matter now?