It did used to be that all MixedFleet and no EuroFleet / WorldWide fleets wore hats, but on the introduction of the new generation 787 and A380 WW also wear hats - just marketing really, to signify the A380/787 as something special. They also had special tasting menus in F on the A380, since discontinued.
I don't think females under MF contracts are offered trousers as a uniform option, its skirts only, I think.