I don’t think there’s any official information on purshasable cash shop costumes yet, although it’d be pretty weird if there weren’t any in the future.
Anyway, about them being class-locked, this is just speculation but if you take a look here you can see there are some items listed as [Gender] Costume [Number], which don’t seem to belong to any known class but are divided per base class (Swordsman, Archer, Wizard, Cleric). There’s many of these specially for Archer and Swordsman. [Gender] Costume [1] is the base costume for their respective Class/Gender, and then you have the rest which are variations. So yeah, all of this is just speculation but you can see where it’s going. I don’t believe those costumes belong to any new unreleased classes because if you take a hard look you notice quickly how they are all based on the basic class clothes. I don’t really know either how they plan to use these, if at all. They could very well be abandoned designs (unlikely).
I also like your idea of some cash shop costumes having special visual effects and animations, for skills or just as a social tool. I’m positive this will be a thing based solely on the existence of the cosmetic sub-weapons that already come with animations (and even sounds) that add nothing gameplay wise, but are just fun to use.
I’m so naive I had forgotten a lot of F2P MMOs have timed cash shop costumes… I’m too used to being treated with decency as a customer I guess. So yes, a thousand times this.
PS: I just remembered the costume system in RO2LotS where there are two types of costumes. Both are permanent but one type comes with stats and slots you can only get from RNG gachapon. I trust IMC to avoid this formula but it’s still quite troubling.
