Thanks for the reply Svetoslav.
It's a real pity that this is not supported on a per library basis since it has so many business cases that it would suite. (Same goes for document libraries)
Use Case: Company Director Images
For me this would work better than creating a bunch of content items in columns because it's more structured based on the template it uses. Having the template alone makes it more powerful becase you have absolute control over what each part of the HTML is going to do.
A custom widget is also an option yes, which is what we ended up doing and using Thunder made it far simpler, but Thunder is missing some things like the designer doesn't allow you to automatically put in a rich text editor for certain public properties. (The image selector based on a Guid type property is great)
The list control wouldn't have worked as smoothly either, because you run into the exact same problem where adding custom fields (I imagine) adds them to all lists.
I wondered whether this could be achieved through a different data provider, but it seemed like a long shot and way too much work for the budget we have for this particular task.