While it could be a lot of work to modify Theater View, we might be able to add a page or two if we knew what to do.
I really think that increasing the functionality of the Cover Art folder would go a long way in improving Theater View. It would be the easiest to implement because you would not need to add any pages or drastically change the UI. The way it would work is the same logic as pulling Season or Series cover art so you would not need to reinvent the wheel with much new code. Plus, it could be implemented a little bit at a time. You could provide stock images, but it would also allow users to customize any images they wanted themselves fairly easily.
For example, start with Genre. Add a Genre folder to /Cover Art with stock images for a dozen or so Genres. Something like these: http://i.imgur.com/4yaSxRX.jpg In Theater View, every time the Genre tag says "Action" it would pull the "Action" image instead of fanned cover art or just having text. There would be a stock image if the Genre does not match any images. Users could change, add, or delete whatever images they wanted for specific Genres just by editing the /Cover Art/Genre folder.
From there, you could add additional folders, like one for MPAA Rating, Codec, Channels, etc.