...categories

I think it'll be useful for people who prioritize certain items over others.

I feel like this would cause an awful lot of lag, having to not only check that an item is on your WL but also which category it's in and what color the outline is supposed to be. It's also not something I'd use (I already have CSS that overrides the outline color so hopefully it would hide the differing outline colors)

I don't honestly see how this would help either? If you prioritize certain categories, don't buy from the others. If you get an item from a quest or something, regardless of what category it's in, you should keep/use it.

I love using the wishlist feature, but I think this is unnecessary. Just use categories to prioritize things :P