As a maintainer of RDF module, I don't have much confidence that the module provides the reliability we need for Drupal 8. We don't have a solution for compound fields (such as addressfield). Not all core field formatters are tested, to say much less of contrib field formatters. And we have criticals that haven't seen any major movement in many months.
In the meantime, Google has announced that it will consume JSON that is embedded in pages using <script> tags, and other search engines have followed suit. As I outline in my companion blog post, this is preferable to HTML data formats (RDFa, microdata) for a number of reasons. The ones relevant to this issue are:
- It would mean we could use the same pipeline for REST’s serialization and HTML data
- It removes complexity from the field formatters and theme layer
- It makes it easier to replace the implementation from contrib
While this is a large change in terms of the description on the Drupal 8 box, I'm fairly certain it will actually require less work than getting our RDFa up to snuff and has a better chance of being reviewable by other people, which this work hasn't really been in the past.