We have just incorporated a few additional tags that should qualify your articles to appear as article type "rich pins" on Pinterest.
It seems however, that you need to apply for these rich pins on a case-by-case basis. As a first step, the page needs to validate here:
The preview image doesn't get displayed unless it has already been pinned before, but for the purpose of validation this is not necessary. Also, some of the fields are optional, so no need to worry about them as long as you get a green check mark.
Then, as a next step, you can apply to get them on Pinterest by clicking on the link next to the validation confirmation. We haven't actually tried doing that, so if any of you are interested to submit a couple of your best pages please let us know how it goes.
This could open up some exciting possibilities and I can't wait to hear about your experiences with this feature!