Tauqeer Aziz shared a screen shot with me on Twitter of Google AdWords testing a sitelinks layout that has a “more” link that drops down to show additional sitelinks in the overlay.
Here is a screen shot of the test:
I personally cannot replicate this and all I get is the normal sitelinks AdWords design on desktop. Of course, on mobile, Google recently switched sitelinks to be a carousel format to show up to 8 sitelinks for one ad. So I guess this is a way to get 8 sitelinks for one ad on desktop?
Forum discussion at Twitter.