This could be interesting - Facebook's testing a new ad unit which would display content from multiple advertisers within a single ad collection.

As you can see in this example, the ad includes content from two companies within the same unit, with the bottom bar branding alternating on each frame within the carousel.

Facebook confirmed the test to Digiday and provided the following statement:

"We are conducting a small test that groups product recommendations from different advertisers into a single experience. We will evaluate if it creates value for people and businesses before deciding whether to expand it.”

It's not clear exactly how this new promotional unit would work - whether the costs would be split evenly between the associated brands, how brands would participate, or how much control they'd have over the partners they're displayed with (as Facebook is displaying these based on product recommendations, not on brand-advised groupings).

It seems more aligned with on-platform discovery, similar to recommendations in Google Shopping or Pinterest, but framed as an ad. That would mean that Facebook will be looking to charge for the additional exposure (they're not charging during the test), though there does still seem to be quite a bit to work out before an expanded release.

Still, it's interesting to see how Facebook is looking at such promotions, and seeking to expand discovery on the platform. The benefits, you would think, will either need to come from reduced cost, higher exposure and/or audience responsiveness, so at this stage, Facebook seems to be merely testing to see if audiences even like the format in the first place. From there, The Social Network will be able to better frame their pitch for the potential product, if they so choose.