In regards to people who keep trying to make creative excuses for Quiet's outfit, Kojima has already admitted that its going to be her outfit for the whole game. He talked about it on his Japanese podcast (see below).
Nope, sorry to disappoint but Kojima said that she will be wearing that as her main outfit during the game, but that there's a reason for that. My bet? Her skin has octo-camo so she needs to be naked to use it.
And yeah she speaks Japanese fluently, she was on Kojima's podcast talking about 3D capture and stuff (that pic with all the cameras). Won't hear her voice in the game though, since her character can't talk.
The way he explained it in the podcast made it sound like that's not the case. He said he knows people are gonna ask why is a sniper naked, that would only make her more visible in the desert. And he said that there's a reason why she does that, but he can't tell yet. And I think the black paint around her eyes disappearing is a hint of what her secret ability is.
As if his 'reason' for her outfit is going to be anything other than an ad-hoc rationalization. He can make her power work however he wants, but big surprise this one is going to require her to be naked. Whoops, sorry, not completely naked obviously, she can still wear a bikini and ripped nylons. Why can her legs be covered by nylons but her chest can't be covered by a tank top or shirt? Why don't actual pants or combat fatigues work but nylons do? Oh but I shouldn't complain, surely there's going to be a well-reasoned explanation forthcoming, there's no way Kojima simply wanted the female sniper's design to be sexually gratuitous, he's never done something like that before...
Side note, even if Kojima hadn't already admitted it, the history of the production process makes it pretty clear it was always the plan.
This fan site post talks about how Quiet was created (sourced from Kojima's twitter posts/pictures).
Making of Quiet in MGSV. Done 3D capture shooting on both face w / & w / O make UPS, body, & Arms & legs separately. We did Also 3D capture Miss Stephanie, the Actor for Quiet in MGSV, both her ​​face and body.
But she was one of the few who got that full-body treatment, this
fan site post, commenting on this
English production podcast, said "Quiet is one of the new characters who had a full 3D scan. So body and face were completely recorded, unlike characters like Snake and Kaz." It's pretty obvious why this dichotomy exists for the body scan; they're not going to spend all that money on tech and full body scanning if Quiet's only going to lose her normal clothes for a few scenes.
Also of note is that those earlier pictures (2012) of her in full combat uniform was while Kojima was testing out full body capture tech to see if he wanted to build one for his studio.
Stephanie with a gun. Testing This was only but was good reason to build Our Own 3D Studio cap.
And then finally,
from that same round of tests in 2012 is this picture of
Stephanie in a bikini. Why would they even need to 'test' for that unless they were already planning on that being her outfit, which they were, and which Kojima has already admitted anyway.