The provided Goodreads widget gives minimal customization such as image size, widget width, widget title size and whether you want additional things like title, rating etc. The code already exists (on Goodreads) so WordPress would have to make minimal code adjustments.
I just wanted to add my voice to this. I’d really appreciate being about to add a customisable widget to my blog. I’m not currently using the Goodreads widget, because I can’t alter it so that it looks right on my blog.