How about they're usable by anyone but only after the player has cleared a tough Stone Sea Sky trial for that respective job? So if you see a BRD in a BRD bikini you know they're probably not the reason the group failed to skip Soar that time (actually, it might be your own if you're staring at their bikini instead of your buttons...)
If it's really hard there could be PFs which specifically demand participants show up in their swimsuits.
Suggestion not entirely serious. We do need more swimsuits in general though if we're headed for the water; now that the old summer ones are in the cash shop and a lot of the craftable ones are in short supply, there's a bit of a shortage on my server.
