I have several other things I need to work on and not a lot of time, and was hoping someone else might be able to tackle this, or know if it is even possible with what is presently exposed to addons.
Basically I want to replicate the functionality of the Crown store where cosmetic items like costumes and hair styles show a 3D preview on your current character when you click them.
It looks like there is some sort of 'canPreview' variable that may link to a previewId of some kind. It may be possible to spoof, ideally without having to build a database of every item equivalent ID in the game, which would probably not be possible without more in-depth datamining since so much is no longer on the store to look up...
Anyway if it is totally impractical feel free to ignore this.
So question, why do you want a preview? You already own them, so you can simply equip the costume to see how it looks. If the issue you have with that is you want it to revert to your current look when you exit the collections screen, then you could simply add a button that equips the collectible as 'temporary' and when you exit the window, re-equips the old costume. Or, possibly simpler, do it like the dye window - you can equip any costume and when you exit it asks if you want to keep it.
1) Having it shown in the preview window like the Crown store ensures that you get a good view. No UI elements in the way, plus you can spin your character around and maybe even zoom.
2) No costume equip animation, which is probably possible to cancel but still annoying.
Additionally, being able to try on different combinations of costumes, hair, makeup, etc. without all the world seeing your character change constantly as they do when you actually equip them, which is also annoying.