After seeing the intent by developers and artists to create iTunes LP and iTunes Extras for their music, Apple has opened up the availability to develop these features to third parties. However, automatic submission for iTunes LP and iTunes Extras is not expected until early 2010; in the meantime, it's still a limited process and uploads must be performed manually.
If you're an iTunes contributor and you're looking forward to developing an iTunes LP of your own, Apple has posted several resources for Extras & LP, including a best practices guide, a development guide, asset delivery tips and a testing guide.
There's also templates to get you started, and documentation on the TuneKit framework used by iTunes LP and iTunes Extras. These make extensive use of the WebKit framework, while using many new web standards.
Are you going to be more interested in these features since it's now open for development? Let us know in the comments below!