Machinist Lunchboxes Should Match Weapons - It is WAY past time.

[Macleod]

The reason the aetherotransformer does not change appearence to match whatever gun you have equipped is it was specifically made by Stephanivien for you, it's one-of-a-kind and custom made for you using the MCH's Guild's own theories on magitek, so it's natural weapon stores do not sell different ones.

That sounds like a stupid lore excuse to half-ass their weapon design. It shouldn't be any surprise to SE that people want to glam stuff and MATCH. Making a stupidly rigid design choice like that is tremendously short-sighted.