"I cant go adventuring in the clockworks like this! my shield doesnt match my shoes!"
often i've found that my shield just doesnt match my gear or looks pretty plain. shield costumes have been suggested a million times before, and nice though that may be there are other alternatives, though non quite as simple

so my suggestion is adding a colourising accessory for shields, probably only in the general colour variants (dusky, royal, heavy, divine, etc.) that switches the default skin for an alternative colour
yes there are problems with this approach, such as needing a half dozen skins for each shield, though as they are all less then 20kb and recolouring a picture isnt terribly difficult i dont see that as being a huge problem, just annoying for the devs

secondly shield accessories, which has actually come up far less often in these forums than i was expecting, probably due to the obvious difficulty of handling positioning since shields come in a huge variety of sizes and the clipping issues associated with the shield designs
still it would be nice to add some decoration to a shield
- ribbons / medals / seals
- sashes (like the aegis one)
- trophies (claws, wolver tails, teeth, robot parts?)
- extra armour plates
- whatever else would be good on a shield (flowers, emblems, fancy glowing patters)

final point, not shield related
the half dozen accessory types (in the basic colour variants, but not special ones like divine or prismatic) that are available during character creation should be removed from lockboxes and sold in haven bazaar, probably for copious amounts of crowns