Traditional School Girl Uniforms.

[Morningstar1337]

Why are people so keen to have to pay for stuff that should be in the game....

For one, the Online Store profits are confirmed to go into development, for another, in this case. a paywall would ensure that only those that really want it and could actively use it are more likely to be seen with with it and thus lessen the population of adventures actually wearing it for those that care about immersion (though TBH I find that argument having some gatekeeping vibes as there ARE people that want to wear more silly outfits like the snowman/frog/moogle costumes and literally anything from the Gold Saucer).

That said regarding immersion in general I actually think RP spaces might be more likely to retain it if only because the people there would likely have a reason to be using certain gear and because if you're RPing with others, that would already ensure you try to make your character as much a part of the world as you can, making the use of some glamours less common outside of certain easy to avoid areas like the Quicksand.

Plus the Online Store already sells a Schoolgirl uniform, which would also play a factor into whether or not SE makes an outfit explicitly in the same archtype of what OP wants as opposed to something that would have other uses like the Sailor shirt