The fact that it requires learning a new API makes it a non-trivial feature, engineering-wise IMO.
I haven't looked into the API or what it takes to integrate it, but I assumed (bad habit, I know) it wouldn't necessarily be rocket science. Aren't most API's relatively simple to use compared to the actually building of an app?
Plus, if it causes a huge increase in users and tire-kickers, it seems an app would get more chances to show off their sexy features anyway.
I think the most non-trivial thing would be integrating with the current site sign-on. Issues such as an existing users that decide to sign on with facebook (which is linked to a different e-mail address) could become a problem on the backend.