Google appears to be testing a design change to its sitelinks feature on search results pages, which makes the experience a bit more interactive for users, and lets sites offer deeper pages within the feature.
Moz and Hyperlinkx Medai CEO Jon Cooper both shared different instances of the feature on Google+.
We haven't been able to replicate the experience here, leading us to believe that Google is just testing this updated experience, but it looks like an improvement to me, so hopefully we'll be seeing it roll out soon.
Google does run about 20,000 of search experiments a year, so you never know.
#MozCast Feature Alert - Spotted yet another call-out box for the 1st organic listing. This one has boxes around all of the expanded site-links and adds an expansion arrow that shows more links (screenshot is the expanded version).
Haven't seen anyone talk about this yet, so I'll just come out and say it - Google has just introduced a new brand SERP pack with drop downs for each sitelink/category.
However, it's not just for big brands, it's being implemented across the board.
EDIT: There's a lot of testing going on right now and not everyone is seeing this like I am.