I don't mind the new armor(or BDSM suit if you will). As far as I know, being a specter is a solo job that requires doing a bunch of other things than shootouts in the open. While being in the alliance and with Shepard she was basically assigned to only two things, shooting the enemy and protecting those behind you (the tank in other words). When your main job is to stay in the line of fire and soak up a ton of damage you don't necessarily need to move around a lot, so there is no reason to NOT use the sturdiest armor you can find, heavy and clunky though it might be.
However, as a specter, you are practically a 00-agent. Sure, there is a lot of fighting in this profession, but there are also investigations, infiltration jobs, work where being a walking fortress isn't always a good thing. Maybe her new threads are made to catch enemies off guard, enemies not expecting a tough-as-nails soldier. Maybe she needs to be able to run very fast for a longer period without being weighted down, chasing smuggler bosses and the likes. Maybe she needs to be stealthy and quiet as minx in other situations
One thing people need to remember is that heavy armor isn't, and never was, part of Ashley's character. Being practical and good at her profession is. Using the plates was most practical in her previous line of duty, but now she needs both mobility, speed AND sturdiness.
Say what you will, but her new outfit is a fine compromise between armor and sex-appeal if you compare it to Miranda's work duds.
The armor is mostly un-plated, tight-fitting and thin, sure, but it is still armor and probably more robust than it appears. Maybe it has the latest shield generators hidden in it's shoulder pads.
Ashley's hair on the other hand....Meh! I'd prefer if her hair was tied up, which would be PRACTICAL!
COuldn't she at least use a hair clip or something?!?!
PS.
"Well, if Ashley's skimpy, light-armor is so practical, then why doesn't Kaiden wear lighter armor too, huh?!?!"
If you honestly care so much how Ashley looks, he's probably dead in your game by now ;-)