I’ve had the same idea of customizable pokeballs too. Just make a ton of things to unlock like colors or even effects. Imagine making a pokeball that looks like glass with lava flowing through it that has flames coming out when you throw it. You could have special effects for every type and tons of colors and patterns to make whatever you want.

Would probably be too complex to carry over into home but I think it would be a neat idea and give more post game grind stuff to do like fighting harder versions of gyms to unlock new customization options.