Just a bunch of stuff that I thought about that would add to the experience.
1) Rugs in guildhalls (either placeable or a floor pattern).
2) Sprite food alchemy machine to replace one of the alchemy machines in the guildhall (instead of two of the same which yields no benefits).
3) Real-life purchasable plushies of the battle sprites (trust me, a lot of people would buy it, I asked).
4) 3D printed figurines of our knights (using a chosen loadout and import it into a 3D modeling program, auras will probably have to be ignored) with color as an extra cost (probably) and extra for the battle sprite (probably).
5) (more if I think of any)
actually, why not have 3d models of the knights and the different armors and stuff like tf2 does? That couls pave the way to people being able to show off custom gear, and even make spiral knights fan animations on programs like blender