There should be some cosmetic items available via Primal, Forge, and Grim sparks.

Why?

Because it's been shown/known that the drop chance of each type of spark depends on the theme of the level you're playing in. However most people end up only exploring a limited fragment of the Clockworks by doing near-exclusively only runs that are profitable/boss runs.

Some easy-access Costume Armors might be one good way to encourage people to do the rest of the CW as well. And it might give off the impression to new players that making your character look good/special (thus adding to their overall enjoyment of the game) is actually easy and within their reach and doesn't NECESSARILY have to involve investing a whole lot of money or time in the game or toothpicking people repeatedly in LD or even risking becoming a pretentious old sourpuss in the process.

As for what these cosmetic items should look like? Well, I think that a few otherwise-impossible reskins/recolors of existing armors wouldn't really be a bad idea, and neither would a few gag/joke costumes.