I've seen this referred to as an Article teaser.
This seems somewhat related to progressive disclosure (which I know you're familiar with), except that complex functionality isn't being hidden, but content itself.
This can also be related to and can work with the Inverted pyramid of journalism:
This style is also referred to as BLUF (Bottom Line Up Front)
- It saves reading burden by reducing the amount of text to get the gist of an article
- It allows more room for other content
- It may allow for tracking the effectiveness of writing by tracking how many users engage with the full article
I don't know of any hard research as for its effectiveness. If anyone knows, please post.
I'm interested to know if there's any sense of anticipation or reward that users feel from this interaction to get more granular information.