There has been absolutely no information released or demonstration of any possible future add on API to date. If they had an API for creating and modifying the UI, they would have used it to build and maintain the existing UI. But the UI appears to be incredibly rigid and hard to update, making it difficult for the development team to make changes to existing UI elements.

Any type of addon UI appears to be a pipe dream at the moment. And I don't expect we'll see one anytime soon.