2D GUIs evolved over nearly two decades of mainstream usage and even longer research. As a consequence, today's GUIs and the rules, after which they are created, are much more complex than, say, cell phone UIs. So, a good OOUI Kit for a 2D GUI target will be a lot more difficult to implement than a kit for cell phones. However, apart from certain traditions in 2D GUIs, I can't see anything, which makes it different in general. Assuming I didn't overlook something, it is possible to implement an OOUI Kit, which creates concrete 2D GUIs, which are at least very close to being on pair with current GUIs in terms of comfort, efficiency and ease of use. See the 2D GUI example for my thoughts, how to manage the complexity.
For several reasons, often, most applications of the same type look and act very similar. It is possible, that an OOUI Kit creates an UI, that is better than these traditional UIs. However, customers might be used to these interfaces and want to stick to them.
As the idea behind OOUIs is customizablity, the Kit will propably allow the user to configure the UI to follow the traditional examples. But this requires time and knowledge, which the user might not have.
One way out of this problem are pre-configurations: The Kit may allow to load a configuration for a certain app from a file, which the user could have downloaded. However, this gives certain Kit implementations an advantage again, which is contrary to the goals of the OOUI interface.
A better solution is a stylesheet, which is specific to a certain target environment, but not a Kit implementation. These stylesheets could ship with the app.