I don't understand the current design. They are also artwork providers, why do user-added plugins only share one position in the search panel and named as “plug-in", but the original plugins have separate position and have name?
I think that although in most cases the providers download artworks automatically, sometimes user needs to show all the results from the providers and pick the most suitable one by himself.
Due to my somewhat poor network, I found that the search for Artwork seems to be in a single thread, with the first provide getting the image url then the latter provider starts running. Wouldn't you consider changing to a multi-threaded operation to speed up the search action?