Sometimes dancers I know wear such garments and, if they're wearing a different bra, might not be where I know they were. I think pantsuits are not only attractive and flattering, but particularly suitable for Swing dancing. Pants of any kind are just fine. For the mechanics of dancing, pants have no negative qualities. Long skirts are fine if they're loose enough to, at knee level, pass a bit farther than to the backs of the thighs.
Long skirts can also be a nuisance if they're cut so that they fly high.
Bell cuts work well, though. But not tight ones. Extremely short tight skirts are usually not a problem to dance with but can be a nuisance for the wearer. I find that short skirts that flare are best not only to dance with but to watch, even those that are cut to expose nothing but leg. Jewelry, in particular, should be selected with extreme care.