Frosty today announced that there are going to be a lot of new things available for us to play with in the Chapter 10 content update:
The UI Skin ArtAssetIDs have been expanded. We'll be releasing another 400 or so art assets that can be replaced, bringing the total to around 650. After this, about 90% of the game will be skinnable.
The corresponding UI Skin Art Pack will be around 5mb with all the new assets.
The movement / resizing dictionary will be filled out. Instead of just modifying the layout of the toolbar, you'll be able to tweak the layout of any of about 250 panels and widgets.
You can read his full post here