Facebook is no longer the under dog in Online Advertising. In a Few year they will be the dominate Online Marketing Channel.
They just implemented Re-Targeting, Conversion Tracking, and a little known feature called Audience Tracking "A Gold Mine for online marketers", as soon as they find a way to crack the user intent market "keywords" Facebook will reign supreme.
My suggestions for user intent is: Facebook shouldn't try to be the search engine, but create a content network, and become the first AD a visitor see after they complete a search and land on the publishers' website, and track that incoming search intent "why Google is hiding incoming Keywords", and allow advertisers Retargetng based on previous search terms on Facebook or other sites in their content network.
If Facebook works with publishers to determine the intent "keywords" of a page Facebook can tie intent search phases with Facebook users and delivery related ads on the publishers' site, across the content network and on Facebook.